For years I have always loved the strip bar piano scene...
...and I know Billy is the center of the scene, and I think, along with a few other scenes or comments (Boogie choosing 'Presley' over Mathis or Sinatra), we're supposed to see the impact that rock and roll (and music in general) has had on these guys.
And I know people like to dump on Guttenberg, and I'm not saying he's any great shakes as an actor (even if I loved him in this), but the dance he does with the stripper is priceless! The stiff legs and the arm movements, his confidence...love the whole scene!
"You're a cookie full of arsenic...I'd hate to take a bite of you" - J.J. Hunsecker