A(n) historian joke

While cleaning his room, jrandall went on a tangent about historians and asked for people to finish the joke "An historian walked into a bar..." I made five attempts. Four were terrible. One was sort of funny, if you're into historian jokes:

An historian walked into a bar and the bartender offered him a beer. The historian looked puzzled. "You're allowed to serve alcohol in this establishment? What about the 18th amendment?"

The bartender said, "Are you crazy? That was repealed in 1933!"

"According to some," said the historian, "but I don't subscribe to revisionist theories."

Maybe I'll submit it to Prairie Home Companion...