'The Funniest Joke in the World' is a famous extended sketch from
Monty Python's Flying Circus, concerning a lethal joke which supposedly caused havoc during WW2. The joke itself is "Wenn ist das Nunstrück git und Slotermeyer?
Ja! Beiherhund das Oder die Flipperwaldt gersput!". The sketch was at the end of 'Wither Canada?', the second episode of the first series, broadcast in October 1969.
'Monty Python - The First 200 Years' reveals that it's a mixture of genuine German and gibberish, but not what it actually means. My rusty knowledge of German and Babelfish later, I can state with wobbling uncertainty that one possible English translation might be:
"If is the now-struck git and slotmaster? Yes! Behind-dog it or the flipper-forest kaput!"
(Inebriated Poet kindly points out that 'Oder', capitalised as in the first writeup, is a river in Germany (in which case the above translation would go '...dog it Oder the flipper-forest..' which, as I'm sure you will appreciate, gives the joke a new and sinister slant)
Which appears to be something to do with pinball. According to a native German speaker in the alt.monty-python faq a more strictly accurate translation would be:
If is the now-piece (git) and (Slotermeyer)? Yes! (Beiher)dog that or the pinball wood (gersput)!
I hope that makes more sense.