185 xxx walk into a bar

Not really improv theater but done by a quite a few troupes, and fun when done well. Get a term, e.g. Elephants. The lines go like this:
185 elephants walk into a bar.
The bartender says "Sorry but we dont serve elephants here"
(witty line thats the reply of the elephants )

Players basically come up with an instant joke about 185 whatevers that enter the bar. As already said, not really theater... But it is an exercise to come up with an instant reaction reagrding the term.

References

http://improvencyclopedia.org/games/One_Eighty_Five.html