BOYS ONLY! WHY WOULD HE DO THIS? THANKS.?

1. I was walking in the school hallway & this boy called dan, Was coming the opposite way & the dorr said' push' but i 'Pulled' and yeah and he then smiled alot and gigled a little and Blushed a bit when he saw me lol.. 2. i came school in a really shortish skirt and dan was walking past me and my mate was walking like 7 feet away from me (Just to see if he woudl do anything) and he DID! he looked me up and down with a smirk/smile on his face! (Legs mostly) Also i spot him looking at me a lot. 3. he also hummes a tune to some randum song? when ever he sees me and when he is in a distance and so am i he looks at me ...Why would he do all this? diffrent reasons are good thanks.