In an interview with NPR, Kimmel explained the origins of his signature signoff. We had a bad show The guests were bad, and I was feeling pretty bad about myself at the end of the program. And I decided to say, for the amusement of one of our producers who was standing next to me I want to apologize to Matt Damon. We ran out of time. And he got a kick out of it, the producer, so I just started doing it every night to amuse him. Matt Damon was just the first name that popped into my head. I was trying to think of an A-list star, and somebody we absolutely would not bump if he was on the show. The legs on this bit are unbelievable to me. I mean, people laugh every time I say it. Repeating the same joke every single night, youd think eventually people would get tired of it, but they dont.

While the show-ending line kept getting laughs, Damon himself got into the act when Kimmel's then-girlfriend, Sarah Silverman, enlisted the "Bourne Identity" star to appear in the video for her self-explanatory 2008 song, "I'm F***ing Matt Damon".

Kimmel turned the tables on Silverman and Damon in 2009 when Damon's old pal Ben Affleck appeared in Kimmel's response song video, "I'm F***ing Ben Affleck".

This was followed by Kimmel sidekick Guillermo appearing on the set of "The Bourne Ultimatum" only to get beaten up by Damon, who was not too thrilled to see Kimmel's show promoting the upcoming movie as "The Guillermo Ultimatum". Says a ticked-off Damon: "I mean, are you f***ing kidding me?"

Damon got his revenge when Kimmel's fake lover Affleck was joined by John Krasinski, Matthew McConaughey, Patrick Dempsey, Keith Urban, Sting, and Rob Lowe to eject Kimmel from the Handsome Men's Club with the big twist that it was Damon who engineered the entire thing.

In Kimmel's trailer for "Movie: The Movie", a dejected Matt Damon (inexplicably costumed as a bunch of grapes) winds up being cut from the star-studded faux-movie, leading him to send out this pithy response.

In 2013, Damon finally managed to get revenge on Kimmel for all those bumpings, kidnapping the host and hijacking the show, with the help of Andy Garcia and the late Robin Williams.

Kimmel fired back by sending Guillermo to crash the junket for Damon's sci-fi flick, "Elysium", which he took over by promoting a movie HE made, called "Estupido." As Guillermo explains (in Spanish, via subtitles), his film is "about a stupid man who has a friend named Ben, who is also stupid. And he's from Boston. He is very stupid."

Kimmel made Damon pay for his takeover when he and the rest of the cast of "Monuments Men" visited the show, with Damon shuttled off to the side to sit in a tiny stool while the rest of the cast sat in couches.

Finally, the pair decide it's time to try to repair their relationship when Damon visits the show wearing a Dr. Phil disguise. The whole thing, however, is a setup to show a clip of what happened when Kimmel and Damon attended couples counselling. Try to contain your shock, but it did not go well, especially when Damon reveals that he lives "at the show, in a dressing room," in perpetual hope of not being bumped.

When Ben Affleck returned as a guest, he took to the stage wearing a ginormous suit that surprise! actually contained Matt Damon, smuggling him onto the show until Kimmel figures out the pair's scheme.

Kimmel was incensed when he cut to a remote in Vegas, where his Aunt Chippy was playing blackjack until she was accosted by "Matthew from South Detroit," who was actually, as Kimmel described, overrated actor and simpleton Matt Damon.

Damon and Kimmel attempt to give couples counselling another go, but Damon's feelings are hurt when Kimmel is dismissive of his idea for promotional "Bourne" bumper stickers, such as the one that says "Honk if you're Bourney."

When Kimmel decided to run for vice-president, Damon took the low road in a faux political-style attack ad designed to trash-talk the host. Declares Damon solemnly: "If Jimmy Kimmel f***ed Ben Affleck, who's he gonna f*** next? America?"

After Emmy host Kimmel lost to John Oliver at the 2016 Emmys, Matt Damon joined Kimmel onstage, crunching an apple while gloating at Kimmel's loss, reminding him how humiliating it is to have lost "and now you gotta stand out here for the rest of the night in front of everybody." He asked the crowd to try to make Kimmel feel better by giving "the big loser" a round of applause.

Following the New England Patriots' stunning comeback at the 2017 Super Bowl, Damon once again tried to sneak his way onto the show, this time disguised as Pats QB Tom Brady. It doesn't take Kimmel long to figure out Damon's ruse. As he's being escorted offstage by security, Damon yells: "I won the Super Bowl and I won your stupid show!'

Jimmy Kimmel and wife Molly McNearney welcomed their first child a few years ago, and the couple are now expecting a second but is Kimmel really the father? Damon believes HE's the father, and they all appear on Maury Povich's show (with Maury played by Martin Short) to take a paternity test. "We dont know if you're a boy or a girl, but you have a choice of daddies," Damon tells the fetus inside McNearney's belly. "One daddy could be an Emmy loser the other daddy could be an Oscar winner! Do you wanna play with daddy's Oscar?" Tracy Morgan drops in for a twist ending to prove who's REALLY the father.

So will the feud rear its ugly head while Kimmel hosts the Academy Awards. You can count on it. "Im going to do everything I can to make sure that he doesnt win or doesnt know that he won," says Kimmel of his plans for Damon. "My goal is to keep him offstage." Responded Damon: "I'm just sad Chris Rock isn't hosting the show, someone who's actually funny."

More here:
Jimmy Kimmel vs. Matt Damon: Anatomy Of An Epic Hollywood Feud - ETCanada.com