I got hit on once. Kinda creepy actually, cause I noticed this guy stalking me for a few blocks. I stopped around a corner and pretended to text on my cell. The guy stopped as well, and started small talking about christmas shopping etc. We walked 4 or 5 blocks, I kept my responses to a minimum, and told him I was picking up my girlfriend from work. The guy was polite and nice though, so I kinda felt like an ass giving him only one syllable replies. Also I'm from Norway where people are a bit more, well frigid, so I though alright, this is the US, home of the brave and all that, maybe this is totally acceptable behaviour. At the last ped crossing before my gf's work he said "So, uh, do you want to head back to my flat for some fun?" I rejected politely and told him I'm straight, to which he replied "Oh, that's okay, I'll do all the work".
This happened in San Francisco but it was downtown, not the Castro. I had scruffy 1-month beard, an Adidas hoodie with food stains, cheap GAP jeans and dirt on my boots from camping, so I really can't see why the guy would hit on me.