Why the hell do my friends always think I base everything on sexual things? (and a little rant about a friend(?) I'm starting to hate)

Today at school I was feeling bad, I was more quiet and silent, since my friends are the type to make stupid jokes, I normally put up with all of them, but today was one of the days where I was at my limit, if I heard any little joke I would definitely tell one of them to go fuck themselves. So far so good, but then a friend of mine came up to me and showed me a video of a practically naked guy, saying "Be happy", I stared at her for three seconds without understanding, I'm not that kind of dude, Girl, go find something to do, no, I don't want to know if your cousin broke up with her boyfriend, nor am I going to explain the damn subject to you because you weren't paying attention to shit.