i would guess the percentage is over 50. There is a LOT of partying going on at the U. I know because i've been to the parties. (yes i am a drinking byu fan) maybe i'm way off and the drinking part of the students aren't part of the muss.
that said, the students are waaaaaay more obnoxious than the players. i guess that usually goes for fans in general. at the same parties, i talked with lots of yewt players. they always knew i was a BYU fan and were generally respectful about that.