i've only been a few times, but i picked up on a few types of gay guys and the ways they make themselves known:
1) the shy gay guys look at you sideways or from under their eyebrows or hat rims, then look away very quickly in order to not get caught, but realize they've been caught and you can see panic on their faces as they speedily walk away.
2) the cocky gay guys look at you casually, too casually, while doing that annoying model puckered lip thing with their mouths and sucking their cheeks in. often accompanied by the gay tilt (you know, when the head falls back some and slightly to one side, in order to give the appearance of being in an ad for armani or something)
3) the average gay guy looks at you rather boldly and directly when he doesn't realize you're watching him do it, because you're using 3 inter-reflecting mirrors and he's looking directly at you.
4) the jane fondas don't require gay dar.
5) the older gentlemen of a certain age who are confirmed bachelors and came of age in a time without open homosexuality who walk right up and congratulate you on your achievements, not realizing that they're hitting on you (or at least acting like they don't realize it)
6) the jealous gay guys who throw hateful looks at you and don't care if you seem them do it or not
7) the horny gay guys who cruise you in front of the whole room by standing next to something and resting eternally between two sets that never happen
8 ) the chattering gay guys who aren't quite shy and aren't quite average... they are a combo of 1 and 3. they use the terms dude and bro uncomfortably while clearing their throats between independent clauses.
9) the straight acting muscle bunny. nearly impossible to detect, until you realize that anyone that concerned with masculine beauty (namely his own), is pretty likely to be gay. these vary: look for matching athletic shirts/shorts on some. others are too "clever" to be this fashionable. they tend to talk about pussy alot and very loudly. watch whether or not he's as quick to check out a woman without being prompted by his obnoxious friends.
10) the new gay on the block who is getting checked out by numbers 1-9 and is given away, not necessarily because of himself, but because collectively everyone else has sniffed him out. he is often looking around himself because of all the eyes on him. might be jumpy.