How can you tell when a guy is looking at you "by accident"?

This guy seems to look at me a lot... and I seem to catch him a lot too. Except I don't know if it's just a coincidence that I'm catching him looking at me then looking away quickly. I keep telling myself that he's just glancing and nothing more. Sometimes he looks down at his phone then looks up at me then looks back at his phone and usually when he's laughing, his eyes will wander towards me. It's just that he's VERY good looking (the kind of guy every girl would go for) and I'm pretty (not cocky at all though) but I wouldn't think that he would go for somebody like me; that's why I keep telling myself that it's all just a coincidence.

So... Coincidence or not?

How can you tell when a guy is looking at you "by accident"?
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