David Cameron might have been chastised by the speaker for his un-parliamentary language when he accused Ed Miliband of hypocrisy, but he managed to get away with calling bald Labour MP Liam Byrne "Baldermort".
However a Number 10 source later admitted the prime minister needed to be careful when using gags.
Cameron's put down came two weeks after he called Labour MP Dennis Skinner a dinosaur in PMQs: "It's good to see the honourable gentleman in such good form.
"I often say to my children 'no need to go to the national history museum to see a dinosaur, come to the House of Commons at about half past twelve'."
Cameron has previously got in trouble for his 'flashman' - the bully character in Tom Brown's schooldays - style put-downs. The prime minister was attacked as anti-feminist after he repeatedly urged a female Labour MP to "calm down dear."