I don't have anal sex like you mentioned doing it from where you poo from. That's not sex, it's an abominable act. Sex is never gross for me. I love and enjoy it.
Sex is only gross when you're doing with someone you don't have any emotional feelings for. Also, it can be gross if you're doing it with a partner who's not good at keeping himself or herself neat.
To me, sex isn't gross but I can call it gross and even add disgusting when it's been done from where the poo comes out. I can't imagine someone saying that they have anal sex, I saw it as a disgusting habit.