Keyboard Cat is an Internet meme. It consists of footage from 1984 of "Fatso", a cat (now deceased) owned by Charlie Schmidt of Spokane, Washington, wearing a blue shirt and "playing" an upbeat rhythm on an electronic keyboard. In reality, Fatso was manipulated by Schmidt.
The clip, originally posted to YouTube as "Charlie Schmidt's 'cool cat'", has gained popularity by being appended to blooper and other viral videos as if to "play" that person offstage after the mistake or gaffe in a similar manner as getting the hook in the days of vaudeville, usually accompanied with the title Play Him Off, Keyboard Cat or a variant.
Above information taken from Wikipedia.
BBLiveShow has made a large number of references to Keyboard Cat. Quite often, when the Keyboard Cat music is played, Justin Robert Young will extend his arms straight out and imitate Keyboard Cat's playing style.