I don't get why the guys would laugh at me.

Yeah I'd have to agree that if you're hot then it's probably rude or lewd comments "man what if I got my hands on her...".

There's also the possibility that what you think is "not doing anything weird" is seen as _avoiding_ any sort of interaction. A lot of attractive girls come across as incredibly stuck up (maybe they actually are stuck up- I don't know) but if they think you're deliberately ignoring them then a rude comment could salvage their pride and prompt a laugh from their friends.

Ok not that I do this but I'm pretty sure I know what this is lol. If they are lookin at you and laughing while they're walking by then one of them probably said to the other that he would do you or summin along those lines and then they giggle cuz, well its funny to them lol. I mean if you're hot or whatever and they do that then that's probably what's going down