In the late 1970's John Denver at one point in his concerts would ask any Jehovah's Witness in the crowd to please stand up. Once they were standing he would play the National Anthem! Hillarious.
Here's a trick you can try. Call a local Kingdom Hall. When someone answers "Hello, Kingdom Hall" say "Ha! You just said hello to a disfellowshipped person!" and hang up.
Or, get a bunch of friends together for a flash mob at one of the conventions. Then start clapping at really inappropriate times during the talks. Leave right before security asks you to.
Anyone got any more?