This is why I LOVE Realjock! Some VERY VALID topics come up.
Sometimes I wish all gaymen had a green plasma fuzz around them that only other gay men could see - wouldn't life just be too damn easy then?
Back to reality!
MrSoftball, you got it right - the EYES!!! Eyes are the window to the soul and your eyes give away your true intentions...Having being a personal trainer at the Univ of Virginia (which, BTW, is one of the gayest universities according to polls) for a long, long time, I had to realise that there were a few different looks I'd get owing to the fact I was a little older than most students and hence far better built than most:
I wasn't obviously gay, and esp. NOT while I was training others or myself in the gym, however, outside of the Univ. environment all bets were off and some students knew I was gay. Those who were gay fell into cat (2) and (1) above, those who were straight fell into mostly category (4), (1) and (3) respectively, although, those in cat (3) were very few and far between.
So, take notice of how someone looks at you - it's pretty easy to know when someone merely glances at you and has NO interest, and if someone looks at you with disgust, that's easy too. Telling the difference between (1) and (2) above is prb the hardest one, esp. you you are "newly" gay, meaning "newly" wanting contact with other gay men for whatever reason. And it it can be just as hard for a "veteran" gay guy in a mostly straight gym - EVEN in San Francsico!!!
There are MANY very open-minded straight guys out there who are VERY friendly BUT fall in Category (1) and NOT category (2) - this will always be where your experiences or lack of can make it difficult ot easy to know if he is straight or gay. It's all in the eyes and the length of eye contact and the repeated eye contact....
Just use common sense and try and think it through BEFORE your dick takes over as the center of reason and decision!
Remember, that person may be wondering the VERY same thing about you - this whole topic is especially hardest for those still in the closet. Once you actually get out and frequent with other gay men, it becomes pretty easy to spot a gay guy. Well, mostly....
So that really is half the story! Once you establish the guy is gay via whatever means, he probably wont want to talk to you anyway! LOL.....