McLoser?

Patrick Dempsey, who plays Derek aka McDreamy on Grey's Anatomy, was in an 1987 teen chick flick as a geek. "Can't Buy Me Love" is basically a reversal of "She's All That" except instead of a bet, the loser boy buys the popular girl. Of course the usual stuff happens, he changes for the worse, betrays his friends, loses the girl, the secret gets out etc. etc. But happy ending and worth a watch because at age 21, Dempsey is really cute.