It has to stop
Straight guys have to stop saying that they're bi or gay when they're not!! What if they're doing it to a guy who's secretly gay himself and he takes it as an opportunity to hit on the straight guy? Then the straight guy gets creeped out and the gay guy's feelings are hurt.
I'm saying this because it happens to me ALL the time. If you're straight don't say you aren't. At least not around me.