1: Does he try to impress you?
2: Does he make jokes around you? Or possibly playfully insult you?
3: Does he always laugh at your jokes? (Even if they are dumb ones?)
4: Does he suddenly like things you like? (Stuff he never really liked before)
5: Do you ever catch him staring?
6: You pass him in the hallway. He:
7: When you get paired up in a project does he moan?
8: When he tries to impress you and fails he...
9: Does he always talk about something cool he can do or something cool he's done or accomplished? (Such as "I'd played basketball for 5 years and I am on a team)
10: Last of all, does he playfully mess with you? (Such as a light punch on shoulder with a smile)