Expression used when someone is going off on a conniption fit. The rage is depicted as the size of an elephant or having the rage of a lion (ie. Simba from Lion King).
Girl: I cant believe that f-in m-fer cut me off. What the eff is wrong with his f-in lane?!?!?!
Guy: Whooooaaaaaaa......... down Simba! He is a 1/2 mile in front of you!!