The term is actually "jumping the SHARK" referring to the painful last episodes of Happy days in which arthru fonzerelli aka 'the fonze" jumps over sharks on water skis while simultaneously wearing his trademark leather jacket. Jumping the shark occurs when a show has hit and alltime low and has to do something drastic and crazy to maintain its viewers and keep them interested.
Example- Hey did you hear that Sean and Christian are moving troy/ macnamara to LA for the new season of Nip/tuck? Wow I hope there not jumping the sharkwith that one.
When a group of guys go to mack on a group of girls, the guy who jumps on the grenade is the guy who goes after the fat chick in the group to clear the way for his friends to go after the hot ones. Usually guys take turns