- He doesn't care so much or at all about his appearance or dress, or he has long hair or had it when you met him and before you convinced him otherwise, although the only exception might be longish curly hair.
- He's below 30 years old, born in the US, and not out or known as gay to his close friends and lives in a big city in California or other liberal place.
- He does not glance in an attractive guy's direction even for the smallest instant briefly in passing -- even if otherwise obviously preoccupied with, say, talking to you. It could be generalized, that a guy who doesn't check out other reasonably good looking guys is straight. A reason why I think this is a good one is: I know that I've passed women -- with their smaller figures, long hair and lighter footfalls or heels -- without glancing up for a moment. I.e. you can tell someone's sex from far away and if a guy's not interested in a closer look -- it is after all just looking -- he won't bother if he's straight and a guy is approaching, just as I don't when a woman is approaching.
Of course, I'm out, and so I have dropped any pretense of attempting to mask who gets my 'closer glance' preference. My guess is some closet cases may have developed the counter to this, which is basically to check out every youngish woman he passes and purposely not the guys, at least when he's with his wife. But god, wouldn't that just take any remaining joy out of life? It's just so sickeningly soul crushing to even think about...