I wear a sleeveless or tank top to the gym all the time except for the rare occasions when I'm behind on laundry and have to wear a t-shirt. Quite a lot do where I lift. In fact, I find it's really only the people who aren't in shape that wear t-shirts. 100% hetro here...
No guys have hit on me yet at the gym.
Then again, girls haven't yet either...lol
I find it a bit odd when people wear blue jeans to the gym or work out in a polo shirt, but I'm there to work out and not get my rocks off on watching other people. I think worrying about what other guys are wearing is more along the lines of "gay".
I like to see my muscles work when I work out, simple as that. I usually wear track pants, but if I'm doing legs (and not doing deadlifts that day), I'll often wear shorts that day too so I can see.
Heck, I wear headphones the whole time (anti-social?) and a fanny-pack to hold my wallet and mp3 player (too many locker thefts). I think a fanny pack is much "gayer" than a tank top, but it serves a purpose for me in the gym, so I can care less what others think of it, lol.
Ever watch those MMA fighters? Most fight topless, often wear tight, tight spandex shorts, and then hug/mount each other. Out of context - that's gay to the extreme, yet truthfully those guys are the furthest things from it (much respect to the MMA guys).
(Although I really wish those "Condom.com" sponsers would find a better location to advertise their company that right on the guy's butt. :\ LoL)