Finally thought of how Harley should react to being punked.
He stands shocked for a moment, realizing Bull had tricked him, but the eponymous mad elf won't be so easily beaten. He traipses up to the bar, takes the phone from Bull, and holds it to his ear (the fake one, of course). He then spits out some smokin' freestyle rap that gets everyone in the bar bobbing their heads. He then hold the phone out to Bull with a drek-eating grin and says "It's for you."