I told this to a work-mate, but first turned it into a (literal) shaggy-dog story. Seemed to work better (he slapped himself for a couple of minutes, then asked me to repeat it so he could e-mail it to a load of friends).
The long version: -
A salesman is visiting a town for the first time. On the way to the hotel he asks the cab-driver what there is to do in the town.
The cab-driver thinks a bit before repling, “You could always go to the zoo!”
The man thanks him, checks into his hotel, then goes to look for the zoo. Fortunately it’s well signed and a few minutes later he walks up to the entrance and asks for a ticket.
“That’ll be $20.” says the zoo-keeper.
“Twenty?!” gasps the man, “Is the zoo that good, then?”
“Best zoo in town, sir.” the keeper answers.
So the man pays his money and goes inside. The first cage he comes to is completely empty. Well the man is a little peeved, but he just puts it down to the animal being cleaned or something and moves on. Only the second cage is empty too, and the third, and the forth. Soon the man is running past row after row of empty cages, getting more and more frustrated, until he comes to the last cage. Inside is a single, small dog, yapping shrilly.
By now the man has had enough, he storms back to the entrance, bangs on the glass and shouts at the zoo-keeper, “I paid $20 to see some goddamn animals and there’s nothing in here but one damn lap-dog! What’s the meaning of this?!”
The keeper looks up from his paper and replies, “It’s a Shih-Tsu.”