it could mean he is shy and love you
Another guy will express interest in you by talking to you, smiling at you, winking, perhaps stealing glances at you, etc. === ===
It does not necessarily mean anything - he may not be interested in your smiling.
By asking him.
he loves you
He might be imagining you making him a sandwich, its really difficult to guess based on that information
he glances at you constantly
he probably likes her and most likely he will think she's out of his league especially if the girl is pretty..
try smiling or a small wave and see what happens if you get no response write him off as a creeper.
You will catch him/her taking glances at you!:)
Usually when you catch a guy looking at you and smiling it's because he might like you!! If he's a shy guy, then he might be too scared/nervous to talk to you and sticks to smiling and looking your way. If you have the courage go and talk to him!! :) if not, then you can make a friend introduce you guys! Good luck!
Have you tried smiling back at him? Try it, you'll see that if he smiles back, it's a good sigh!
He is stupified with lust. --- or he is just thinking about something else and happens to be looking that way. ;)