Great slasher flick from the early eighties, about a boy that freaks out after seeing his family being killed by a man in a Santa Claus outfit.
The boy grows up in an orphanage with the punishment-loving Mother Superior, and when he gets a job in a toystore he has to put on a Santa Claus outfit he totally looses his marbles and sets out on a killing spree to punish everyone that has been naughty.

Because that's what Santa Claus did according to his Grandpa.

This film is fantastic, i don't know how many times i have seen it. Will Hare is uncanny in his role as the Grandpa.