David Brenner He enjoys a good joke, but uses observational humor in his act. Vinnie Favorito plays off his audience in his act, but personally laughs at long jokes. Photo by K.M. Cannon. Dave Russo analyzes the structure of a good joke to find that unexpected surprise. Photo by K.M. Cannon. Carole Montgomery says slapstick comedy is her favorite, "but I wouldn't go onstage and slip on a banana peel for a laugh." Photo by K.M. Cannon.

We know what makes us laugh at the stand-ups working Las Vegas comedy clubs. But what makes them laugh? Surprisingly, the type of humor most comedians are known for isn't what tickles their funny bones offstage.

"I love a good joke, but I don't do them," says David Brenner, who co-headlines with George Wallace at the Flamingo's showroom this month.

In the late '60s, Brenner, George Carlin and Robert Klein were the first comics to popularize the "Did you ever notice how ...?" observational humor dominating today's comedy stages.

"I just started talking about observations because that was my natural sense of humor," says Brenner, "But I love jokes -- if they're really good."

Brenner heard his favorite years ago, from actor Jack Lemmon.

"It's brilliant," Brenner says, "but you can't even use it anymore because of the censorship that's going on in comedy."

Brenner says it's also one of the fastest jokes he ever heard.

"OK, here it goes," he says. "Two Irishmen walk out of a pub in Dublin. ... It could happen!"

Onstage at O'Sheas, Vinnie Favorito specializes in the type of audience-interaction improvisation popularized by Don Rickles. (That's a polite way of saying he's an insult comic.)

"I'll ask Mexicans where they're from," Favorito says, "L.A. or Texas."

But what cracks Favorito up at home? Again, jokes.

"I love the long ones," Favorito says, "the ones where you can keep someone's attention and it's funny all the way through."

Favorito's favorite begins with a couple living on the 33rd floor of a condo. "And it ends with the guy in the refrigerator," he says. "But I can't tell you the middle because it's too long to print."

Favorito says he regularly exchanges jokes with Drew Carey.

"We'll call each other and say, 'I just heard this great joke,' " he says. "I've never heard of a comic who didn't like a good joke."

Indeed, nearly 100 of America's top comedians -- including Brenner, Carey and local favorites Rita Rudner, Carrot Top, Pat Cooper, Amazing Johnathan, and Penn & Teller -- take turns telling the same dirty vaudevillian joke in the 2005 movie "The Aristocrats."

"I think comedians like jokes because it's where everybody started," says Penn Jillette, the film's executive producer. "Any big illusionist you talk to has a fondness for card tricks. They'd never consider doing them in their show. But that's where they started when they were 12 and there's still an affection for that."

Dave Russo, who performs at Funny Business at Desert Passage, says he still analyzes the structure of good jokes when preparing observational monologues.

"You have to have people thinking one thing, then turn the corner on them," he says, providing a favorite example: "Last night I was at a dance recital for six hours. Six hours! My lap was killing me."

Local funnywoman Pam Matteson likes jokes about animals.

"Not, like, two dogs walk into a bar," she says.

Matteson tells her favorite whenever a snotty Vegas dog-park person inquires about the breed of her Yorkies.

"I tell them they're police dogs," she says. "And they go, 'They don't look like police dogs.' And I'll say, 'They're in plain clothes.' "

Riviera Comedy Club performer Carole Montgomery says she's "not a joke person." Yet the humor that cracks her up hardest isn't the risqué observational humor she's known for, either.

"It's slapstick," she says, singling out the scene in the Marx Brothers' "Duck Soup" where Harpo impersonates Groucho.

"That to me is the funniest thing ever," she says. "But I wouldn't go onstage and slip on a banana peel for a laugh."

Jillette says the phenomenon of enjoying what you don't do for a living cuts across all career lines.

"You have very, very heavy writers who like to read light mysteries," he says. "If you invite the guys in Barry Manilow's band to come over to your house and play music, they don't play Barry Manilow tunes. And there's a lot of really wonderful chefs who like junk food."

The only local comic we interviewed to claim identical comedic preferences, onstage and off, is George Wallace.

"I laugh hardest at typical, everyday things," he says. "Stupid signs, like, '24 Hour Fitness, open 6 a.m. to midnight,' or people asking you stupid questions in the grocery store, like, 'What are you doing here?' 'What am I doing here? I'm (expletive) hungry!' "

Ultimately, though, what we find funny about our favorite comedians, is also what they find funny -- at least on some level.

"I think you get out there and talk about what makes you laugh," Brenner says, "and what you think is funny. And you just hope they agree."