Every man has his moral backside which he refrains from showing unless he has to and keeps covered as long as possible with the trousers of decorum.
Notes from Wikiquote
As quoted in Der Witz und seine Beziehung zum Unbewussten [Jokes and Their Relation to the Unconscious] (1905) by Sigmund Freud, as translated by James Strachey (1960), p. 100
Variants
Everyone has a moral backside, which he does not show except in case of need and which he covers as long as possible with the breeches of respectability.