Two clowns are eating a cannibal...

Two clowns are eating a cannibal, one says to the other, "I think we got this joke wrong."

This is an example of the deconstruction of a different joke. The original joke is cannibals eating a clown, and then saying that the clown tastes funny, but in this version the clowns are the ones that are eating the cannibal.

Probably, the humor in this one lies in the unexpectedness of the joke being backwards. The person that hears the joke and has heard the other joke might not realize that it is being told backwards until the punchline occurs.

If you had not heard the punchline I expect that this joke wouldn't really be funny. The absurdness of clowns eating a cannibal is sort of funny, but it is not random enough to be really funny.