When you shove your arm up someone's ass so hard that the anal cavity changes purpose and its sole purpose is then to be a receptacle (pipe) for your fist.
Man, never go to that gay club on 5th Street, they have a thing with fistpipes.
An action that in recent years has taken the place of a high five. A fistpound occurs when two individuals reach out and touch fists. This usually occurs after someone has accomplished something hard or has made a funny joke.
