I’m a terrible DJ (unless you count success by the number of people you can force off the dance floor with one track, in which case I’m a total mix master), but I’ve worked with enough DJs to know the tricks of the tracks. And one of those tricks is the old left-it-at-home routine.
When somebody requests a song you don’t want to play, you say “Excellent song! I love that one.” Then you pause and say “I think I left it at home.”
Now, Djs will have no excuse, becasue the new Pacemaker app will let you spin and mix tunes from Spotify’s huge gazillion-song library.