A hot tub filled with naked men. And, like, hot water of course.
It has been said (and confirmed by a Mr. Brendon Urie) that mansoup is used as a sort of initiation into the Fueled by Ramen family. Pete Wentz held a mansoup party at his home with the members (no pun intended) of Panic! at the Disco.
Oh how the fangirls squealed.