Okay here's one I just made up, although I assume it's probably not original.

Knock knock
Who's there
Nobody
Nobody who
...

Sitting on the side of the highway waiting to catch speeding drivers, a State Police Officer sees a car puttering along at 22 MPH. He thinks to himself, “This driver is just as dangerous as a speeder!” So he turns on his lights and pulls the driver over. Approaching the car, he notices that there are five old ladies — two in the front seat and three in the back - eyes wide and white as ghosts. The driver, obviously confused, says to him, “Officer, I don’t understand, I was doing exactly the speed limit! What seems to be the problem?”

“Ma’am,” the officer replies, “You weren’t speeding, but you should know that driving slower than the speed limit can also be a danger to other drivers.”

“Slower than the speed limit?” she asked. No sir, I was doing the speed limit exactly... Twenty-Two miles an hour!” the old woman says a bit proudly. The State Police officer, trying to contain a chuckle explains to her that “22” was the route number, not the speed limit. A bit embarrassed, the woman grinned and thanked the officer for pointing out her error.

“But before I let you go, Ma’am, I have to ask... Is everyone in this car ok? These women seem awfully shaken and they haven’t muttered a single peep this whole time.” the officer asks.

“Oh, they’ll be alright in a minute officer. We just got off Route 119.”

The other day, my girlfriend told me she wanted to have a real fairy-tale wedding.

Ever eager to please, I gave her a loaf of bread and left her in the forest.

Thanks!