That’s not something you can say about all celebrities, and it really speaks to Rickles natural talent that he was always “on”.
I think what Jimmy Kimmel shows very well in his tribute is that Don Rickles was authentic through and through.
Even in his advanced age, the man was so quick-witted and observational that you could tell that his mental sharpness clearly aged slower than his physical body did.
All of Kimmel’s stories, personal notes, and anecdotes from other celebrities point to the fact that Rickles was the riotous man in person that he was on stage in front of an audience.