Don Rickles heckles Jimmy Fallon: 'From my heart, I never liked you'

You can't teach an old dog new tricks, but you sure can teach an old comedian new jokes.

Don Rickles proved that even at 89, he can still have Jimmy Fallon in stitches when he appeared on Tuesday's "Tonight Show."

The late-night host introduced Rickles as "a true original legend in comedy, they don't make them like this anymore."

His guest's compliments were a little more scathing, however, as Rickles told him: "You're fresh, you're funny, you're great … I want you to know something. From my heart, I never liked you."

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The veteran comic at least had some good advice for Fallon including to pull his hands out of his pockets, not to come out on stage so quickly, and that his badly injured finger was a "great bit."

He even pretended to get the NBC host confused with Jimmy Kimmel, and joked that he was leaving to go over to ABC.

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Rickles has been a frequent guest on "The Tonight Show Starring Johnny Carson" and "Late Show with David Letterman" since 1965. More recently, he's become a comic idol of Fallon's and was one of Letterman's final guests before his retirement in May.

Genuinely collapsing into laughter during their latest interview, Fallon said he "wanted to write this stuff down — we're on five nights a week, we've lots of time to fill."

But he finally got embarrassed when the infamous comic told him, "I can't picture you making love," and later when Rickles told him his comedy was "real honest without popping a monkey."

Watch the video.