Mum jokes...
They've mostly been done, so you have to challenge the conventions of the genre (Oooo, hark at me...) a bit to get them to work.

Two which genuinely stuck in my mind were the following:

In a computer room at Uni, me and a couple of other people finishing essays in the middle of the night, having a bit of banter and getting a bit giggly. Suddenly, a lad who lived at the end of the corridor burst into the room in his dressing gown: 'Can you lot not keep it down! I can hear you from the end of the corridor. Don't you know people are trying to sleep?'. To which someone instantly replied 'Yeah, that's what your Dad said...'

Secondly, involving the mum herself. There was one lad at Uni who had foolishly confided that his mum used to be a semi-famous actress in the seventies and eighties. Photos were duly looked up on the internet and she was declared to be a bit of a hottie. As a result, he took the brunt of the Mum jokes. However, when she eventually dropped by and we were introduced to her, there was an awkward moment when she said 'So - I hear you all think I'm a 'milf'?'. I did a proper pint-splutter...
(SnowyTheWereRabbit the Leporid from Hell, Thu 11 Feb 2010, 16:53, 4 replies)

That first one
I don't get it.
(The Boy Monders I have ginger bits in my beard., Thu 11 Feb 2010, 17:04, closed)

It's suggesting...
...that that's what his dad would have said, had he been stuck somewhere down the corridor whilst you were doing his mum.
(SnowyTheWereRabbit the Leporid from Hell, Fri 12 Feb 2010, 0:04, closed)

Didn't really work, that one.

( disasterprone "Pyjamas caused the Holocaust", Wed 17 Feb 2010, 13:41, closed)

Yeah. Probably had to be there..
...and quite immature
(SnowyTheWereRabbit the Leporid from Hell, Wed 17 Feb 2010, 18:50, closed)