Sitting down for a chat at New York City's 92nd Street Y on Monday night, the comic had a tart two-word reply when asked about The Tonight Show host.
"F--k him," xfinity.com reported Kimmel as saying.
With Jimmy Kimmel Live moving up from 12:05 a.m. to its new 11:35 p.m. time slot and about to go head-to-head with Leno in the ratings for the full hour, the funnyman had some fightin' words for his new rival.
After lavishing praise on David Letterman, Kimmel was asked by event host Bill Carter his thoughts on Leno, whom Kimmel took to task for the allegedly shoddy treatment he felt Jay had given Conan O'Brien in 2010 when Leno's primetime comedy show bombed and he wanted his old gig at The Tonight Show back from his successor.
Kimmel told the audience that after he did a scathing impersonation of Leno on Live!, he was invited by Jay to take part in a 10 on 10 segment for his program. But what Leno didn't expect was Jimmy to continue the ribbing and embarrass him on his own show.
Reflecting on his appearance, Kimmel said the smackdown "was probably my proudest moment."
"People it turns out, really don't like Jay Leno," the comedian offered fondly. "We have not spoken since that time."
Kimmel's not the only one who's got a beef.
News of Jimmy's Leno-bashing comes just days after Howard Stern revived his feud with Leno by blasting Jay's claim to have slashed his salary to save some of his staffers jobs after NBC-imposed budget cuts on The Tonight Show.
"It's all horse s--t. It's bulls--t. It's a smokescreen," the shock jock said about the story. "Here's what it really means, and you can take this to the bank: Jay Leno is a scumbag. That's what that means. He's a spineless maggot. Jay wanted to cut staff. He's embarrassed to do it. He didn't want to come off as a bad guy."
Stern, who also works for the Peacock as a judge on America's Got Talent, acknowledged he didn't have any specific information to back up his allegations, chalking it up to his "bulls--t meter."
But after telling listeners on Aug. 21 that an angry NBC exec threatened to reprimand him, saying he was "uninformed," Stern so far appears to have gotten away unscathed, particularly since he added that he loves his job on AGT and had high praise for NBC, calling the higher-ups there "nothing but wonderful."
"I don't answer to anybody. Everybody knows that," said Stern. "And that's why I'm a great f--king judge," said Stern.
Reps for Leno and America's Got Talent were unavailable for comment.
(E!, NBC, The Tonight Show and America's Got Talent are part of the NBCUniversal family)