Not a joke as such, but true old tale.....
"Many moons ago, when Hugh Laurie and Sir Stephen of Fry were just becoming 'known', they were interviewed on a BBC radio show. Mr Fry asked what the foam covers on the end of the mics were called. To which Hugh Laurie said, 'They're called 'Spoffles' and they prevent what's known as 'Popping'.
Stephen Fry, the host and the engineer were all impressed by Hugh Laurie's knowledge and the interview continued.
Years passed, and once again Fry and Laurie were in a BBC radio studio. The engineer said something like he'll just adjust the Spoffle.
Hugh Laurie says, 'The what?' And the engineer explains that this is what the foam things are called.
"'Good Lord,' laughs Hugh, 'I made that word up on the spot years ago in a studio!'"