Worst acts and attributes: After paving the way for Voldemort to murder his friends, James and Lily Potter, by revealing their whereabouts, Pettigrew faked his death by taking the form of Scrabbers (or “Wormtail”), framed Sirius Black for the Potters’ betrayal, and would continue to covertly serve the Dark Lord into the Second Wizarding War.
He earns a high spot on this list for betraying the trust of his friends and getting some of them killed in the process.
The Sorting Hat’s indecision to place him in either Slytherin or Gryffindor should have been the Wizard World’s first clue to how deceptively mischievous Peter Pettigrew could be, and I actually give the self-taught Animagus credit for managing to spend more than a decade of his life as a rat, just not for his reason to.