A "show off" tune should be one from the heart. It's a tune that you play, sing, play and sing, with which you are so intimate that it's as if there's no one else in the room except you and the song. Your audience will know, unless they're a bunch of tin-eared morons. Playing at breakneck speed or singing at the top of your lungs, because you don't know any other way, is often viewed as "without finesse." A grand example of this is Bill Sables playing and singing "Rubenstein" or "Christmas in the Trenches." I was awestruck with the intimacy of the music with the musician. That is what a "show off" tune is ... moonchild