Least regrettable but most unconventional liquid to take a bath in?

Gallium? It's solid at room temperature, but your own body heat will melt it, so you lie down on a solid block of metal and then slowly sink into a melting puddle in the middle of it. It's non-toxic and six times denser than water so you'd be really floaty on it too
- Sounds like something out of a horror film. Your body heat melts you into the material. Then, as heat gets distributed and you have more skin contact, you are no longer generating enough heat to keep the gallium melted.
  You either suffocate as the material solidifies around your abdomen or you freeze to death as the material pulls enough heat from you to kill you.
  
  Actually because of the density you wont be able to sink more than about 1/6th of your body into it.
  
  This was my first thought. Terrifying! Claustrophobia has entered the chat.
  
  Shit
- 150 litres of Gallium would cost $130800
  https://en.wikipedia.org/wiki/Prices_of_chemical_elements
  
  Well that does make it quite regrettable for most people, I suppose
  
  We need to convince the billionaires that this is the cool thing for them to do...
  
  Hmm! Quite the investment vehicle!
  (I'm now just picturing tech bros smugly smiling with bathtubs full of gallium)
- It might act like a giant heatsink tho, making your body cool out as soon as it starts melting and creating proper surface contact. But chilling in 20°C water is also not really an issue so i guess it depends on the thermal conductivity of the skin/gallium interface.
  
  Just use something similar with a lower melting point. Mercury or cesium both do. You're welcome!
  
  I'm sure an Infinite ice bath has an appeal to someone
- You don't want it to get in your body (holes, cuts etc...)
- the physical description also applies to butter
- Missed opportunity for a Saw film

Heavy water - like water, just heavier.
- What dilution? 25% makes you sterile and 50% kills you after a week of drinking it
  
  Don't eat your bath salts. Don't drink your bathwater.
  As a general rule: Just don't.
  
  You have to have 25% and 50% in your body fluids for it to happen, if you drink a glass of 50% heavy water you won’t drop dead a week later.
  
  Wait, would it work as a contraceptive, then?

Maybe coconut water or aloe vera gel, I imagine it'd feel weird but probably not regrettable.
I guess we've got to beat Cleopatra as our baseline with her bath of asp milk.
Marmite would probably veer into the regrettable category, and I'm saying that as a marmite enjoyer
- As a marmite lover, I'd give it a shot.
- coconut water
  in a heartbeat
  aloe vera
  I can imagine this feeling really tingly after a while, though not sure why.
  asp milk
  what is this? I googled and found nothing
  marmite
  I too partake joyfully in that hellish sludge, and have wondered what depths of depravity I would willingly go to to satisfy that dark craving
  
  Wikipedia says donkey milk was used by Cleopatra, not asp milk. Maybe OP meant ass milk and got autocorrected, but that sounds really wrong.
  
  what is this? I googled and found nothing
  Ah I got my history slightly wrong, she bathed in donkey milk and just liked asps (a kind of snake)
- You’ve got two Cleopatra stories mixed up there.
  She was said to bathe in ass’s (donkey’s) milk.
  She killed herself by holding an asp (snake) to her breast.

Oobleck for the experience. It wouldn't clean you, but you'd have a story. Possibly mild regret if it's in a bathtub that you need to clean or a house who's plumbing you're responsible for afterwards.
- I like it -- though how do I get out of it?
  
  Very slowly.

Water based lube.
It’d have to be a communal bath though, and I’m inviting you all, even Hairy Steve.
- Extrapolating from the slipperiness of lube on the floor: this is a terrible idea. People will be bouncing around like pinballs.
  
  This just sounds more and more appealing. Count me in.

Heinz Baked Beans.
- Excuse you, this isn't unconventional at all, 69,000,000 Brits do it every morning
- Baked Beans
- no regrets?
- It seems that you need to go watch Tommy: A Rock Opera immediately
  
  Oh I'm a huge fan.

Sleepytime tea
- My goodness, that's almost a bucket list item.
  Hmm. I wonder how steeped would be best for maximum soothing. Unless it's a heated tub there would be a real art to the timing, even once you know.
- Feel like any resulting UTIs would be worth it for the great sleep that bath would bring

Oatmilk, Tea, Cum, Flavored water (no sugar pls)
- one of these is not really like the others is it?
  
  Flavored water does feel like cheating. It's really just water.
- Cum flavoured water could be a big seller
  
  It’s a hard sell though.
  
  Coconut penis

Alcoholic beverages
white wine (but a dip into red would be interesting)
beer, for the carbonation
champagne, for the bubbles and the decadence of it
Other liquids
sparkling water, a jacuzzi without one
rose water (for those who don't know, it is sickly sweet smelling and very persistent and can be food grade)
oil, like sunflower, olive or any other of the like. After, just scrape you body, like the ancient athletes would do
- I read these to my husband and he said "an oil bath sounds like it would be good for your skin but you'd be all slipping around and unable to get out then you'd drown." While flailing his arms around as a visual aid.
  
  Or if you did get out you'd immediately slip and crack your head open.

Zero sugar energy drinks.
No sugar means its not gonna get sticky, it'd rinse right off.
I imagine a bunch of creams already use the b vitamins you'd get since they love shoving b vitamins in those.
And it'll actually drain when you're done and a quick rinse will get everything normal afterwards.
- coke zero, no question. diet coke? no thank you. Pepsi max? gtfo
  
  Imagine rocking up to the weird bath house all prepped to bathe in Coke and they’re like, “Oh, sorry. We only have Pepsi.”
- Would the caffeine have any effect? Can skin absorb it?
  
  Yup, you’d probably have a bad time

I was going to say heavy water, but TIL that it's not just chonky water. It can be toxic.
- Only if you drink it in considerable amounts. Should be pretty fine for a bath though.
- Like, barely toxic. Table salt will kill you faster.
  One line of evidence for this is a literal mixup at a nuclear plant where they managed to put it in the water cooler for an extended period, with no ill effects.

Macaroni & cheese
- no regrets? You'd just get up and go to bed covered in the stickiness?
  
  Who says I'm going to bed?

Elon his blood. 6L is enough.
- I think 4L is enough for him to go into shock
  
  I just want to be sure.

A mixture of Vaseline and baby oil, just enough to keep it liquified.
- That sounds... messy.... but yes, you will technically be quite clean and fragrant after
- What is baby oil chemically?
  
  I presume they cold press babies, but I could be wrong.
  
  Traditionally, Mineral oil + fragrance
  Mineral oil is also known as paraffin oil and is usually a petrochemical derivative composed of larger alkane hydrcarbons. Fragrance varies a lot.

Vanta Black
I'm gambling that the experience of it would mitigate how much of a pain in the ass the repercussions would be.
Edit: I suppose I ought to have looked before, but this appears to be not the healthiest decision (who'd have though‽). Maybe we'll go with some kind of closest equivalent nontoxic paint?
- Vantablack isn't really paint, it's a coating of nanotubes the size of an atom. I wonder what that would feel like.
  
  Yeah, after I looked at it a bit and saw that exposure to/inhaling nanotubes probably isn't the greatest idea I figured nontoxic paint was the next go to.
- Nice interrobang.
  
  I had no idea a single symbol existed for an interrobang?!
- On the morbidly curious side of things, I do wonder what such a person looks like. You would just notice the eyes and the hair. Everything else would just be stark contrast.
  There's also the whole, "went vanta black face" issue
  
  Vanta black face is only 2d racism.Which is a measurable amount, but incomparable to 3d racism.
- Very fine charcoal powder maybe (and self-contained breathing apparatus).

Milk ?
- lmao, the most rational answer in this whole thread

Cannabis oil
- now that'd be a journey

I'd say perfluorocarbons, like perfluorodecalin. Harmless and clear, but they have huge oxygen absorption capacity, so you'd surely be able to breathe even if you sank your face in it (probably not fun to do so tho).
- Like waterboarding yourself whilst never dying
  
  No, you still die, because a viscous and therefor slow-moving liquid physically can't remove CO2 fast enough from your lungs. Otherwise we'd have lots of premature babies hanging out in jars.
  Unfortunately, in humans CO2 is the thing that gives the "suffocating" feeling, and it takes a long time to actually kill you at modest levels, so that description still applies a bit.
- Very difficult to immerse yourself into these, though, because of their density being about 2x that of the human body.

Honey
- least regretable
  
  The only one that’s physically repulsive to imagine though. It would be so sticky

Oxygen
- There certainly wouldn't be any regrets (because you would not have time to do so before death).
- Would the temperature be reasonable for a human in liquid form?
  
  No. It even passes the critical point at just 5 bars, in case anyone was trying to get clever with high pressures.
  Also, skin becomes very flammable in pure oxygen (at atmospheric pressure), in case you'd prefer that kind of burn.
  
  At 1 bar the boiling point of oxygen is 90.19 K (−182.96 °C, or the temperature of a banana when thrown into liquid oxygen, in freedom units) so lower than this up to freezing point (54.36 K, −218.79 °C) is liquid form. So it should be comfortable for a human to bath in, with the current world tension, clown leaders and right wing extremism on the rise.

A non-Newtonian fluid

Clarified butter

Warm egg custard

Astroglide

Lemon jello.
Just before it sets.
- Like it sets with you in it?
  
  Oh yeah.
  Me mold.

Homeopathic sleeping remedy.
- That's just water. :|
  
  That's the point

$240 worth of pudding.
- That's nowhere near $240 worth of pudding. Give me about 60 gallons of milk, a pile of cornstarch, some sugar, and some vanilla extract and I'll make you over 8 cubic feet/220 liters of pudding. You'd drown.
  Edit: I did the math and I could comfortably make over 50 gallons on pudding on that budget even with maltodextrin and modified corn starch, no heat just mixing.
- lmao, I wish they dived in

Steve Allen on his TV show in the 60s used to occasionally get into bathtubs full of weird stuff. The one I remember offhand was oatmeal.
- I would happily do oatmeal

Hand scrubber wash. You know the hand soap/lotion thing full of beads to scrub your hands clean? Love that. I'd get in a tub of that.

Vegetable oil

Y tho
- 4kicks
  
  Seems like a criminal waste of beer. Unless that's Bud Light.

nail polish that has been sitting out with the lid partly unscrewed for a week.
Or printer ink. Costs thousands.
Edit: missed the regrettable part 😞
- nice try nonetheless

Custard
- Is pudding a custard?