'Old Comrades' at the Carnival

At the 1973 Cologne Carnival festivities, German comedian Jonny Buchardt manipulated the audience into screaming "Sieg heil". Given the age and backgrounds of the various Cologne dignitaries seated in the crowd, this reply had likely been ingrained in their collective muscle memories all the way back in the '30s and '40s.

To put that joke in context: Giving the "Sieg heil" or any other such Nazi salute was, by 1973, not only strictly taboo (for obvious reasons), but also forbidden by law in Germany. While Buchardt's joke did cause a minor scandal, nobody was prosecuted.

Example of:
Freudian Slip