The Death of Eric Cartman - S9-E6
Corrected entry: At the end when Cartman finds out he's not really dead (everyone was just ignoring him), he storms over to Butters and accuses him of lying to him by telling him he'd died. But earlier on, when Cartman and Butters meet, Cartman's the one who told Butters he had died.
Correction: Cartman is a sociopath and can't ever admit fault: Butters didn't tell him he wasn't dead, therefore, it's all his fault.
Captain Defenestrator