WATCH: Letterman, Conan diss Leno

Memo to David Letterman: Let it go already.

Letterman, who’s made a sport of bashing frenemy Jay Leno, was at it again last night — ripping into the “Tonight Show” host with guest Conan O’Brien, visiting “The Late Show” for the first time since Leno reclaimed “Tonight” from him in 2010.

“I think the longer we just sit here, the more uncomfortable it will make Jay,” Letterman said to O’Brien after the host of TBS’s “Conan” sat down and the two men sat in silence.

“You know Jay’s watching right now,” O’Brien said. “You know he’s . . . getting a live feed in a satellite truck right now.”

Then, imitating Leno’s voice, O’Brien said, “ ‘Dave looks unhappy. He’s gonna pack it in soon.’ ”

Letterman and O’Brien then bantered a bit about “Conan” before Letterman again steered the conversation back to Leno. “I’ve known Jay a long time. We go back to the mid-’70s . . . He was funny. He was also a bit of a brat,” Letterman said. “So then, you know, when this [2010 ‘Tonight Show’ incident] came along, I said to myself, ‘Oh, yes, this is the Jay I know.’ ”

Later in the conversation, Letterman again brought up Leno — asking O’Brien about his “relationship with Jay . . . before the felony took place.”

“Occasional phone call,” O’Brien said.