How do I know a guy at the club is not really into me?
Night vision goggles and a crystal ball, plus a copy of "The Rules That Every Gay Man Follows But Nobody Talks About or Tells Anybody About or Even Acknowledges Exists" should cover you.
Truthfully, it always seemed to me that it's all part of some male behavior code and a bar behavior code. I never could follow it, was never interesting-looking-enough to set my own rules, so I opted out of trying after a while. Reading your story makes me glad I never bothered trying again.