Why does this guy follow suit when he sees other men checking me out?

[Anonymous]

He already knows what I look like so why would this guy turn around to glance at me when he sees other men making double takes at me?

[DoggyDude]

The average person is sheepish. When walking through the city, if I see one person stare up at a building, within a numer of minutes multiple people are looking wondering what might be happening and if it is interesting.

So in this case, he's probably wondering what they other guys are checking out and feeling that it must be 'worth a look' himself. I'd guess (and I am guessing).

[Asker]

But he used to have a crush on me and knows what I look like so why bother?

[DoggyDude]

Well if he used to have a crush, clearly he just enjoys looking at you anyway and other people looking gives him a good reason to enjoy what he sees.