A famous, easily-used quote, from which
Isaac Asimov obtained the title for his book
The Gods Themselves. It comes from
Friedrich Schiller's play
Jungfrau von Orleans (The
Maid of Orleans - ie,
Joan of Arc).
The original
German version is "Mit der Dummheit kämpfen die Götter selbst vergebens". Although it does require some training (unless your German is more fluent than mine), using this version instead of the
English translation might spare you lots of trouble with your
interlocutors (unless their German is just as fluent as yours).
Use at your own risk.