pumpkin head
1. A dim-witted or unintelligent person; a dolt. Why did I ever hire that pumpkin head? He can't do anything right around here.
2. prison slang A prisoner who has been beaten severely about the face and head; such an attack itself. (So called due to the swelling of the head that results.) No one went near the pumpkin head after his beating from one of the prison gangs, which had served as a warning to the other inmates. Whatever fellow prisoners might do to you, it's the guards you have to look out for. They're very fond of giving a pumpkin head to anyone to who steps out of line.
turn into a pumpkin
To have to return home or go to bed due to the late hour of the night. (Usually used as a present participle, the phrase is a reference to the story of Cinderella, whose magic carriage turned into a pumpkin at midnight.) I've had a wonderful time, but I'm turning into a pumpkin. I think I'll call a cab and head home.