The “f” word - and no, I don’t mean fuck - is definitely not allowed. I’m pretty sure sissy would be okay, though.
I did once have a story returned for revision, for a scene in which a guy has a sexual encounter with another guy, then regrets it as soon as he orgasms, ending in a homophobic freakout. It’s possible the character dropped that f-word in the draft that was returned, but I can’t remember exactly. I toned down the interaction a bit, and it was approved.
My guess is that if the straight guys on the street make some casual, joking remarks lightly making fun of your character as he passes by, it’s probably fine. If they get genuinely abusive, maybe not.