A phrase that is popularly attributed to a person, even though that person didn't (originally) say it. Rather it was invented for the person, by satirists/impersonators.
Named after veteran impressionist Mike Yarwood, who is famed for invented such phrases.
Examples of yarwoodisms include...
"Billions and billions". Carl Sagan insists he has never said this, and it originates from a Johnny Carson impression.
"I can see Russia from my house". Sarah Palin has said words to that effect, but it was impersonator Tina Fey who said this famous quote.
"Elementary my dear Watson". Not said in any of the original novels, but still regularly used to impersonate Sherlock Holmes.
"Beam me up Scotty". Never said in any of the Star Trek editions (closest was "Scotty, beam me up" in one later episode)
"My name is Michael Caine". A common way of impersonating said film star; it was not until 1983 that Caine said it on film, in Educating Rita (as an in-joke)
"Why can't I quit you?". Not said in Brokeback Mountain, but the product of Russ Parr's parody of the film (on his Morning Show)
"Super smashing great". Although Jim Bowen frequently said each of those word in isolation, he never said that phrase on Bullseye-- it was supplied by Spitting Image. Bowen has used it since then though, as self-parody.
"There's been a murder". According to Alex Norton ('DCI Burke'), this has never been said on Taggart-- frequently used in parodies of the show though.
"Crisis? What crisis?". Jim Callaghan never said that, The Sun newspaper paraphrased him for a headline-- the phrase is still popularly associated with him.
"Let me tell you a story". A catchphrase for Max Bygraves, invented by Mike Yarwood.
"Ssssilly billy". Denis Healey never originally said this, another Yarwood invention.