A metric tonne (1000 kg) should be called a megagram (1 Mg).

A megagram is 1000 kg, by definition. It's symbol is Mg.

In metric countries, we just use the word "ton" as shorthand/slang for it, since it is an easier term and was well known.

The only reason the US calls it a metric ton, is because they have archaic units (long and short tons).

Metric countries don't call it a metric ton.

There's nothing wrong with doing so. Perfectly up to you, and everyone would know how much it is.

I sometimes use millitonne (mt) instead of kilogram to keep people on their toes. I've learned that some people doesn't like to have their weight measured in any kind of tonne.

I noticed this with vehicles. Odo has 100,000 km on it? Nah, it's 100 megameters. It just sounds cooler

Units closer related to everyday stuff are those that stick around. Like horse power or km. People don't use Mm but instead 1'000s of km, even into the million km for cars. Even in space they still tend to use km like for the distance to the moon or sun. Only once the distances get absurdly large is there a shift to either another unit (light years) or the use of different notation (like 3.14E12 m).

Earth's circumference is 40 Mm. 1 AU is 14 Gm. I could get used to this.

Megagram is the official SI term for the weight. Metric tonne is non-SI but happens to be equivalent to a megagram and became the more common parlance (where I am, at least) by historical accident.

I like metric wrenches, if my 5mm doesnt fit I can try the 6mm. Most nuts and bolds are not metric, so I end up figuring what comes next if my 1/2" doesn't fit. is it like 33/64th? 34/64th? 17/32nd?

One magnesium please. yes I'm sure, only one.

What is this metric shit? I'm an American! I measure weight in American units like the hundredweight and the truss and the slug!

Sounds good to me 👍

But then what would a metric fuckton be?

I'm an engineer, and I make it a point to teach young engineers that "a ton" can mean any one of three things:

Short ton = 2000 lb
Long ton = 2240 lb
Metric ton = 1000 kg = ~2204 lb

And which is being used is often not spelled out, but is just known from context, and usually should be clarified. I once nearly got in trouble by thinking a measurement was in short tons when it was actually metric tons.

So my own act of rebellion is to use "Mg" when I'm writing my personal notes.

In Italian schools they teach it as Megagram, since ton is an old term which is non compliant with the SI

After reading the comments, I've noticed a point that is missing from the other comments. We like to measure things relative to other things. Therefore we should use a unit of measure which you can compare the entire range of expected values for that question simply.

For example how far away is my nearest town centre? 1km. How far away is the nearest city? 10km. How far is it across the country? 500km, How far is it across the continent? 5,000km. How far is it around the equator? 40,000km.

By using all km in this case it's easy to get an idea of the relative distances. But you wouldn't measure your height as 0.0018km. Just my own thoughts!

we do call them megagrams?

It's all either Megagrams / hectare or tons / acre in my work...

I've often wondered why the kilogram was not called the gram when the former is commonly cited as the official unit of mass? I guess it doesn't really matter much since it's easy to convert between units. That's sort of the point of metric, but still…