It's not particularly clever, but it is funny.
The best 'your mum' I ever heard of was when a cricketer was being barracked by another player, who said "How did you get so fat?" He replied "Every time I fuck your mum, she gives me a biscuit."
There's a guy at work who never learns. He thinks he's a comedian, and persists in telling mouldy old jokes which weren't even funny when they were fresh.
Him: "What's big and hairy and goes up and down?"
Me: "Your mum."
(The punchline is supposed to be 'A gorilla in a lift', in case you've been living in a cave.)
One day, a bunch of us were gathered in the pub after work, and the lame-o decided to inflict a 'joke' on us. It was a particularly tasteless one about a women's Olympic team who'd drowned after their ferry sank. (I don't mind bad taste jokes as long as they're funny, but this one sucked ass.) I've forgot some of the exact details, colours and numbers, but it doesn't really matter, so I'll just fill in with any old thing.
Lame-o: "I've got a good one!"
My mate Steve (in Sid James voice): "Aren't you lucky."
Lame-o: "No, listen. What's red and purple . . . no, what's orange and purple . . . er, purple and orange . . . I'll start again. What's orange and purple, and has got fourteen tits . . . no, twenty-eight tits . . . I mean, fourteen pairs of-"
Everyone: "Start again!"
Lame-o: "Okay, I've got it this time. What's purple and orange, has got fourteen pairs of tits, and floats in w- . . . no, I mean, doesn't float in-"
Steve: "I'm losing the will to live."
Lame-o: "No, shut up, this is a good one. I'll get it right this time." Assumes a look of intense concentration. "What's orange and purple, has fourteen pairs of tits, and doesn't float in water?"
Me: "Your mum."
General hilarity ensued.
The best 'your mum' I ever perpetrated was in Cornwall. There was one particular school down there whose pupils every driver dreaded picking up. Their particular thing was witty put-downs. Some of our drivers just couldn't take it; Pete would beg us to swap duties when he was due to pick them up. Swervin' Mervin (so called cos he once turned left instead of right out of the service entrance of the Eden Project, and had to drive for miles and miles and miles before he found a place where he could turn his bus around) got a good dose of it. He thought he always got on well with kids, but even he couldn't get on with these little horrors. They were having their O-levels or whatever, and as they got off the bus, he called out "Good luck with your exams!"
One of them turned round and replied "Oh, don't worry, if we don't get any O-levels, we can always become bus drivers."
Anyway, you know how there's always one kid who can't do it, but that doesn't stop him continually trying, and every time his one-liners fall flat, he tries to cover it up by just keeping on talking? There's one in every school. Well, the kids were getting on my bus in the morning, and as I opened the doors, the mouthy kid was saying "Ah, yes, but you weren't doing the electric boogaloo all night."
The other kids said "The electric boogaloo?!?!?! What is wrong with you?"
Without pausing for a single beat, he continued "Or you may have some other way of spending your Saturday night, I don't know." He turned to me. "And what were you doing Saturday night?"
"Fucking your mum," I deadpanned.
The other kids howled with laughter. He just stood there with his mouth open, until another kid grabbed his arm and dragged him away. Those kids never gave me any cheek after that.
My then girlfriend said "They probably don't want to spoil it; it will be a playground legend. That poor kid will never hear the end of it. For years to come, whenever anyone mentions anything to do with buses, they'll be like: 'Do you remember when the bus driver your mummed you?' "
It's not clever, but it is funny.