Play the Game

Even if he's a flirty guy or not, if he says something jokingly like, "Will you marry me?" don't act all weirded out and say no, play the game! Its fun for both of you and it gives them confidence. Say something flirty like, "Yeah, lets go to Vegas baby." or if they say something like "Wanna make out?" just go "Yeah, lets do it right now." and lean in closer to his face, or "Meet me right after class." Trust me, they love it when you do things like this!