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1.
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.
by Amata May 23, 2008