Pulling a practical joke. Before Jeffrey Dahmer was a psycho serial killer, he was an alcholic class
clown at his high
school. Classmates reffered to any practical joke or crazy antic as "doing a Dahmer". Later, it would come to mean "killing, having
sex with, and dismembering a man".
see the A&E Biography of Jeffrey Dahmer for the actual mentioning of this phrase
Joe: Kevin was just doing a Dahmer right in the middle of class
John: Oh my God! The teacher didn'
t stop him?!
Joe: Dude, calm down. It means played a
joke.