Imitation is the sincerest form of flattery!

In a tribute to David Letterman, after it was announced the Late Show host would retire after 32 years on the air, Jimmy Fallon "borrowed" one of the 66-year-old's best bits, his infamous Top Ten List, to create "The Top Ten Reasons David Letterman is Retiring."

Before reading off the possible reasons the comedian is calling it quits, Jimmy took time to remember his previous interactions with the host, including trips to see him in college and the time he guest-hosted.

"I think after Saturday Night Live, he asked me to guest host for him, when he had shingles. I think that's where I got the bug," the 39-year-old joked. "No, not the shingles bug!"

But in all seriousness, Jimmy made sure to get in a few kind remarks, calling his friend "one in a million" and a "hall-of-famer."

Watch the Top Ten List below!