I uttered that line when talking to a musician friend recently and the drummer behind him looked at me with wonder in his eyes and said, "I would never have taken you for a Tap Head."
I'm obviously an undercover Tapper.
Unless you've watched the DVD version with the band's running commentary on the film, you've not yet had the full Tap experience.
Christopher Guest has a wonderful deadpan face. I still crack up over the line, as he's playing a beautiful piece on the piano, "I call this one "Lick my Love P*mp" as Reiner nods his head. Now it's hard to watch that movie because of Rob "Cigarette Tax for the Children" Reiner's fat face in every scene.