Biffism
Coined by the popular character Biff Tannen from the Back To the Future movies, when one takes a known "exit" phrase and switches the ending so it no longer makes any sense. Often used for the enjoyment of obtaining a double take from the person with whom you are conversing.
Instead of telling McFly to "Make like a tree and leave," Biff told McFly to "Make like a tree and get outta here," thus committing a Biffism.