Jon Stewart was back to his old late night hosting routine during a surprise appearance on Thursday's live edition of "The Late Show with Stephen Colbert." CBS

Jon Stewart did a live, epic takeover of old buddy Stephen Colbert's "Late Show" desk in the wee small hours of Friday morning.

Looking like he'd never been away from the late night hosting gig -- either that, or like he couldn't believe he'd waited this long to come back -- the former "Daily Show" host wasted no time in going after what he clearly viewed as hypocripsy on display at the just-concluded Republican National Convention.

In particular, he skewered one of this favorite old targets, Fox News host Sean Hannity. Or, as Stewart repeatedly called him, "Lumpy."

"I'm actually interested in gymnastics ... That will be the contortions that many conservatives will now have to do to embrace Donald J. Trump, a man who clearly embodies all the things that they have for years said they hated about Barack Obama," Stewart said, proceeding to unfurl a series of clips in which Hannity criticized the Democratic president for everything from using a teleprompter to putting mustard on his hamburger -- a condiment choice Hannity slammed as "elitist."

Stewart did his signature slow-burn look at a camera.

"Yeah, you elitist," he pretended to channel Hannity. "You probably eat that fancy burger with your mouth instead of like a real American: Having a magnum fire 'em up your ass, like they serve 'em at Arbys."

But Stewart was just getting warmed up. He showed a clip of the Republican presidential nominee sitting in ornate surroundings at Trump Tower.

"Meanwhile, here's how Lumpy feels about a guy who sits on a literal golden throne at the top of a literal golden tower with his name in gold letters at the top of it, eating pizza [voice dropping to a dramatic whisper] with a knife and fork. How do you feel about that guy, Lumpy?"

Cut to a clip of Hannity  enthusing over a description of Trump as "a blue collar billionaire" during an interview with some of the nominee's children.

Stewart, confiding to the wildly cheering studio audience: "That's not a thing."

Outside that studio, though, many viewers may have missed one of Stewart's longest such appearances since he voluntarily stepped away from "The Daily Show" last August. Because Trump's convention speech went on for so long (at 1 hour, 15 minutes, it's thought to be the longest acceptance speech by a party's nominee ever), all of CBS's programming got pushed back on the schedule. The "Late Show" usually airs at 11:35 p.m., but it was close to 1 a.m. when Colbert finished his monologue and sat down at his hosting desk, only to be "surprised" when a bearded, t-shirted Stewart crawled out from underneath it.

"Normally this time of night there's no one here," Stewart  told him. "I'm usually just sleeping here."

Then: "I wonder if I could talk about the election for a minute."

He could. But only after Colbert made him put on an ill-fitting sport jacket and an absurdly wide, clip-on tie. Colbert crawled under the desk , but reemerged several times when a fired-up Stewart seemed about to swear on live TV. Once he even blasted him with an air gun.

It wasn't all just in good fun, though. Near the end, Stewart turned deadly serious when he criticized the "cravenly convenient" types he says are supporting Trump who they feel will give them back "their" country.

"There's only one problem with that," Stewart said, looking directly into the camera. "This country isn't yours. You don't own it. It never was . . . You don't own patriotism, you don't own Christianity and you sure as hell don't own respect for the patriotism and sacrifice of (the) military, police and firefighters. Trust me, I saw a lot of people on that convention floor with their Blue Lives Matter rhetoric who either remained silent or actively fought against the (aid for) "9/11 First Responders" bill reauthorization. I see you and your [bleeped out].!"

At which point Stewart, who clearly hadn't missed a step when it came to being a TV host, grinned slyly and pretended to wipe the angry spittle off his chin with that absurdly wide tie.