Mad Slut's are guys who hook up with multiple girls and have no real inhibitions. They can mainly be found in the clubbing circuit and can appear on their own or in groups.
Usually they will hook up with a chick very quickly and move on to another. To be a Mad Slut is a good thing in male society whereas females are negatively labled as sluts when hooking up with multiple guys.
Steve: I just hooked up with that blond chick over there next to the bar, i didn't even have to try!
Dean: Your a Mad Slut!
"I hooked in to 3 different chicks last night all at the same club, such a mad slut.."