My legs, the shower is small and I am tall so it's a lot of work to actually soap them up properly. Usually I only bother maybe every second or third shower.
Has to be my back. It's hard to reach even with a back brush because of degenerative issues in my shoulder joints. I tried one of those scrubbers with the two ropes, but it's hard to control. Need a bigger shower so my wife can wash it for me...and get my back while she's at it!
My naval! I'm very thorough when showering - I absolutely hate feeling dirty. But I think the ol' belly button gets overlooked because of how concave it is.
This thread has made me realize how thorough I am about washing. I use a washcloth and the first things I scrub are the backs of my ears and neck, then arms, pits, torso, back, legs, tops of feet, then for last I do butt, crotch, bottoms of feet and between my toes. Then I ditch the washcloth and with just my hands I wash my bellybutton and privates.
So I guess if I missed anything it would be between my fingers and the backs of my hands.