Yippie the Back-Flipping Dog is a pug that performed at the USO show in South Park: Bigger, Longer & Uncut.
Background
At the USO show, while the Mothers Against Canada are preparing Terrance and Phillip for execution. Big Gay Al announces the first act of the show, which is Yippie performing back-flips. Later, when the Mole is spotted trying to rescue Terrance and Phillip, three army guard dogs pursue him with Yippie following. Yippie is last seen on the battlefield, as the Canadians fight the American army.