Corpsing is a British theatrical slang term used to describe when an actor breaks character during a scene by laughing or by causing another cast member to laugh. The term originated when a living actor played a corpse on stage; there was sometimes a temptation to try to make that actor laugh. Corpsing is not a term exclusive to the theatre, but is also used to describe actions designed to cause hysteria in live television or radio.
The ‘Saturday Night Live’ sketches featuring ‘Debbie Downer’ (Rachel Dratch) are also notable for corpsing, as well as the famous ‘Stefon’ (Bill Hader), who only went on one occasion without corpsing throughout his entire five-year stint. Jimmy Fallon is also known for breaking character by laughing.
The Daily Omnivore 