How do guys know that I'm gay?

I can't see your pic very well, but what's happening probably has something to do with how attractive you are and perhaps the way you style yourself (even though most of your generation either look like thugs or hairdressers, if you ask me)... But that's only part of it. I know plenty of good-looking straight athletes who aren't getting blatantly cruised or approached in the grocery store when they're with their Dad!! You're obviously "looking back", and don't even know it. It has nothing to do with your walk or some gay-dar thing or the way you talk, blah blah blah. You're giving these men the "go-ahead" by the way you're looking at them, you're just not conscious of it. If you don't want guys talking to you, then don't make eye-contact. And don't say you're not, either. You cannot possibly know if someone's looking at you if you're not looking at them.