Taken from an episode of The Simpsons where the creators of The Itchy and Scratchy Show add Poochie, a rapping surfer dog to the cast.
Polar opposite of an Urkel (where a terminally ill show was revived by adding the new character).
The Big Bang Theory started with outstanding chemistry by juxtaposing four awkward nerds with one hot female neighbour. Two key elements were Howard's sleaziness (thinking of himself as successful with the ladies but ultimately failing repeatedly) and Sheldon's uniqueness (no further description required). This show was running hot - and yet the writers added not one but TWO Poochies - Bernadette (now Howard's fiancee) totally neutralises the failed Casanova element that made Howard funny, and then Amy Farrah Fowler comes along as a "female version of Sheldon", removing all that was unique and hilarious about the show's strongest character. Series 4 and 5 TBBT are materially different from the earlier episodes that made this show a world-beater.