A theory that states that any girl at the bar who says "I'm not a slut" without being provoked or actually being called a slut...is always a slut.
Aaron: Hey can I buy you a drink?
Jane: No...I'm not some sort of slut!
Aaron: I never said you were.
Aaron(to friend Matt): Did you hear that girl?
Matt: Yeah man, Slut Theory says shes definitely a slut! Go for it!
...later that night after hooking up...
Jane: you must think im some kind of slut huh?