A chin that has a cleft in it giving it the characteristics of a [bum]. Most people will find the bum chin to be very attractive as it has a certain heir to it. Often associated with power and sophistication. The bum chin is a sign of a distinguished gentleman.
People who have bum chins are more likely to be successful and chosen by the opposite sex, for mating.
> John Travolta has an incredible bum chin.
> Steve must be successful, just look at that bum chin.