Good question. Whenever I was in the other position, of a guy seeing some cute girl, I was always hesitant to go up and say something. Because in all honesty, I did not know quite what to say without sounding weird lol. To make it not weird, you have to try to find in. Say if the guy is looking at something at the store that your interested in, walk over and start looking at stuff in the section too. Then when you feel the time is right, make a casual comment about what he is looking at. "So you like those too, huh" or perhaps maybe ask if he can give you advice (even if you don't need it). Although that last one is kind of sneaky, so it's a judgment call :p. I think probably half the guys would find it weird, half of them wouldn't.