To masturbate. An excuse to tell your roommates when you are going to go masturbate so they think you are going to bed.
Tyler- "Hey guys I think I'm going to go to bed early to catch up on sleep"
Matt- "Tyler are you going to masturbate?"
Tyler- "Noooooo...." (Sarcastic)
Matt- "OH! you're not Catching up on sleep! You're masturbating!"