A sitcom character who has evolved over the years suddenly reverts to a caricature under stress
We've all seen it. A long-running sitcom character has evolved over the years and escaped the broad caricatures of his earliest incarnation. However, under stress, he'll suddenly revert to his slapstick characterization from Season 1. In some cases he'll go even broader than that. Often invoked to short-circuit a major change in the show's status quo (because Status Quo Is God), and sometimes never referred to again.