yeah - i think i'd say hey, what's up, you look like you're in a bad mood.
Some people really have no idea how they come across! Maybe he's clueless, maybe you remind him of someone (transferrence) and he doesn't realize he's glaring at you. Maybe he wishes he had your worspace (lol) we just really have no way of knowing what is going on in the other person's head unless we ask.
Best of luck on this!