"And made me want to hate gay people in general for a while."
Absolutely ridiculous. When I came out my family was fine, then a couple of months later my brother said all gays should be murdered. It made me want to hate my whole family, especially my other brother, because they are family and straight just like the brother that said it...flawless logic...
By all means tell the other man to go fuck himself if a mild rebuke doesn't work a few times, but you are concentrating far too hard on his sexuality. If this actually happened, yes he was being far too forward, in which case you should have called over the clerk, told him what had occurred and smiled broadly as the "creature" was escorted from the store.
Edit: As to what happpened here, the man is camp in the first place because he is over-compensating for something he has been bullied about/worried about his whole life. He is throwing it in people's faces and using it as an armour of sorts so that those who insult him have no ammunition, he just camps it up more - similar to black men calling themselves niggers. You say the man then became extremely forward, and that is because of your response. You insulted him and so he thickened his skin and hitched up his armour, he became the ultimate fag. He came onto you even more, really camping it up and insisting that you are gay too so as to protect himself. I know it sounds weird but people are complex. You may gain a little satisfaction knowing that the "creature" is probably telling others what happened and laughing jovially, all the while probably cringing internally and wishing he was the straight white man.