for girls only: turn him on :D

Okay... This may sound a little.... risky, but it shure works, the only problem is if you are very heavy (or maybe... ugly, sorry...) then it might get a liiiittle hard.
Ok, this is best for people who still go to school: You walk straight over to him, casually, and then you sit on his lap and take your arms around his shoulders and pretend that is is nothing. But this only works, though, if the boy that you like isn't a complete girl- hater!
Then you could say, for example: 'boy, I'm tired.' and then just lay your head on his shoulder. Just seem as it is a usually thing for you to do with boys. Do not blush or smile 'dirty...' :) just... be yourself and start a conversation. If he push you of the chair after a while, don't feel hurt. I mean, it is pretty heavy to have another person on your knee... :)
And if he does it right after you sit down or even before, then he is a jerk, AND.. you know that he is not interested, or maybe he just don't want you to sit on him in front of the rest of the class.. But don't make a big deal out of it either, just 'play' that you are mad at him and then send him a little cute, flirty smile... :D