Here's a nice crossword - orientated joke.
( This might be well-known, but I'll chuck it in just in case it's not )
Sit with a newspaper folded to the crossword bit in front of a fellow enthusiast and stare into the middle distance with a frown. Sooner or later he / she will ask what you're puzzling over. As though reading from the paper, you quote : " Overburdened postman " and carry on frowning. Nine times out of ten the other person will ask how many letters, enabling you to deliver the punchline : " Hundreds "