When my brother and I shared a bathroom while growing up there weren't too many issues. He always put the seat down, he never used my hair products and I never used his (why would I blech) but he had complaints. About my hair. About my long hair getting tangled in his toes after I'd brush out my hair and it would get stuck to the carpet (remember 80's bathrooms with carpet.)
It would be early morning, before school and you would hear this "AGHHH HEIDI!!" I knew. I'd try to protest, feebly, but it never eased his disgust. I could have done a better job cleaning up after every time I brushed my hair, but I didn't. It was really only one of a handful of ways that I GOT TO DRIVE HIM MAD! So, I waited for it. And I loved it.
Today I combed my hair out before my shower and as I was cleaning the hair off my floor, I never missed my brother's stinky feet more.