There's this new guy who's started at my job and he has this weird habit of smirking or half-smiling at me whenever he walks past my desk or is in my general vicinity. He never does it when there are other people around (he sometimes stares though) which suggests to me he's doing it deliberately to make me uncomfortable. I'm always just going about my business whenever he does this, so he has no reason to be amused by my behavior or anything. He's never spoken to me either so I don't even know his name. What is the reason some men do this?