With David Letterman announcing he will retire next year, Jimmy Fallon both honored his competitor and stole one of his bits Thursday night. Jimmy did a Top Ten List explaining why Dave is stepping down.

Among the reasons: the time slot was getting too "Jimmy-esque"...and Dave wasn't retiring, he was "consciously unhosting"!

View the entire list - and learn why Letterman once told him, "I'm jealous of your linoleum."