Thigh-Slapper Meaning

(idiomatic) A joke, especially one which strikes the listener or reader as particularly humorous.

Example: 1980 Sept. 29, Roger Rosenblatt, "The People's Analyst," Time (retrieved 18 Oct. 2009):
  Not exactly a thigh-slapper, but not terrible for a psychiatrist joke either.
2003 July 29, Lenore Skenazy, "Bob Hope's Jokes Just Lived For the Moment," New York Daily News (retrieved 18 Oct. 2009):
  "There's a lot of USO girls in Hollywood," Hope mused on his World War II tours. "USO - Use Slacks Only." Ho ho ho. Women wearing pants. Real thigh-slapper.