When an otherwise straight
male is persuaded to, or on a whim in the heat of the moment, engages in a homosexual act of which he later regrets and is ashamed.
Alluded to in the musical number of the same
name in Mel
Brooks' film "Blazing Saddles".
Having shared the intamacy of a small tent for so
long, in the stress of jungle combat, Pierre and
Gustav came close to making the French Mistake on many a steamy
night.