Okay, this is totally sexist, but it had me howling. (Sent by reader Ken.)
A retired guy sits around the house all day, so one day his wife says, "Joe, you could do something useful, like vacuum the house once a week."
The guy gives it a moment's thought and says, "Sure, why not. Show me to the vacuum."
Half an hour later, Joe comes into the kitchen to get some coffee. His wife says, "I didn't hear the vacuum working. I thought you were using it?"
Exasperated, Joe answers, "The stupid thing is broken, it won't start. We need to buy a new one."
"Really?" she says. "Show me. It worked fine the last time."
So he did.