Harris laughed off the pun, but definitely looked more than a little embarrassed.
"Wow, you had that prepared. You got that one ready," he told the America's Got Talent judge.
Mandel hosted the night's festivities, which also featured a Tony Bennett performance, and a welcome from Jennifer Lopez, who's currently enjoying her own Vegas residency. Harris maintains a residency at Omnia nightclub inside Caesars Palace.
The Scottish DJ, 32, posted a pic with Bennett on Instagram, excited to spend time with the 90-year-old crooner.