Perfect Casting: 23 Stars on Screen as Themselves

The Muscles from Brussels shows that he's more than a pretty face and a wicked kick in this drama, which has Van Damme playing an ex-action hero with financial woes who gets mixed up in a bank heist. Who'd have thought that the word pathos would ever be legitimately used to describe a Van Damme performance? —Hillary Busis

Get Him to the Greek (2010)
ET's Mario Lopez gets laughs as one of the many real-life celebs who cross paths with fictional rock tool Aldous Snow (Russell Brand). But this comedy's funniest cameo player isn't from Hollywood at all — it's noted economist and New York Times columnist Paul Krugman, who shares a few supremely awkward moments with record-biz drone Aaron Green (Jonah Hill) in a TV greenroom. If he ever tires of writing Pulitzer-winning political analysis, we hope Krugman considers a new career in stand-up. —Hillary Busis

The Muscles from Brussels shows that he's more than a pretty face and a wicked kick in this drama, which has Van Damme playing an ex-action hero with financial woes who gets mixed up in a bank heist. Who'd have thought that the word pathos would ever be legitimately used to describe a Van Damme performance? —Hillary Busis

The actor once commonly known as Doogie wasn't shy about shredding his wholesome reputation in this stoner comedy — Harris got high on Ecstasy, humped a seat, and stole a car as a stripper-loving version of himself. And as for what he does in the sequel, some things are best left as a surprise to unsuspecting viewers. —Kate Ward

Stewart was so good playing himself in Ricky Gervais' BBC/HBO comedy, he earned an Emmy nomination for Outstanding Guest Actor in a Comedy Series. He lost the award to Will & Grace's Leslie Jordan, but maybe he'll have better luck with that bawdy X-Men-lite script he told Gervais' Andy all about (''I'm walking along, and I see this beautiful girl, and I think I'd like to see her naked, and so all her clothes fall off''). —Kate Ward

The affable American Idol host-turned-Crest spokesman veiled his pearly whites while unleashing a two-minute profanity-laced rant against young Hollywood after being told Jessica Simpson would arrive late to their scheduled E! interview: ''It doesn't make any sense. I got four jobs — hell, I'm more famous than half the people we talk to anyway!'' Hmmm... after this cameo, we're wondering if he could add ''comedian'' onto that rapidly expanding job title. (Second thought, after seeing his attempts at ''standup'' at the Emmy Awards, let's not.) —Kate Ward

David may have inspired Seinfeld's George Costanza, but the comedian took center stage in his own HBO sitcom as a neurotic, awkward Larry David who might as well glue his foot in his mouth. Though David's the bane of everyone's existence in Curb-land, we think he's pretty good. Pret-ty, pret-ty good. —Kate Ward

Arrested Development (2003-06)
Fox's dearly departed cult series was home to a slew of memorable cameos — Judge Reinhold, Dave Attell, Andy Richter, etc. — but the Rocky star made a lasting impression on us, as well as on admirer Lucille 2 (Liza Minnelli), as Tobias' Burger King-loving, free-loading acting coach. —Kate Ward

Before he was kissing Jennifer Garner's neck at the Oscars, Busey was scaring the bejesus out of Vincent's gang after Turtle accidentally broke a sculpture crafted by the wacky, surprisingly Zen actor.

Sacha Baron Cohen's Borat literally tried to bag the Baywatch babe as his wife (Anderson, meanwhile, lost a husband — her marriage to Kid Rock ended only weeks after he reportedly blew into a rage after seeing the film). We'd say Borat had questionable taste, but then again, we're assuming Barb Wire never made it to Kazakhstan.

Larry Sanders found an unlikely admirer in Duchovny, who tried to woo his man-crush with an invite to a beach house and a Basic Instinct-esque peep show.

The trippy Spike Jonze film takes Craig Schwartz (John Cusack) and others inside the mind of John Horatio Malkovich — not to be confused, of course, with John Gavin Malkovich, the actor's real name and identity. (Confused yet?)

The Price is Right host sparred with Happy (Adam Sandler), his charity golf partner, and capped their violent showdown (heh!) with the brilliant phrase, ''Now you've had enough... bitch.'' See what could happen if you don't get your pets spayed and neutered?

Who's better to judge a Derek Zoolander-Hansel walk-off than the fashion innovator and king of glam rock? Plenty of other celebrities appeared as themselves in the 2001 comedy (e.g., Billy Zane, Paris Hilton, Christian Slater), but only Bowie boasted the proper qualifications to ref the challenge. Zoolander wasn't the last time the artist ventured on screen as himself: Bowie also appeared in Ricky Gervais' Extras to serenade Andy Millman (Gervais) with a little impromptu ditty about his stocky size and ''pug-nosed face.''

Comic book legends may be nerds, but it doesn't mean they don't get lucky in the romance department — Lee cited his ''running tally'' with rocker Mick Jagger while imparting some romantic advice to Brodie (Jason Lee) in Kevin Smith's sophomore film. (Lee, apparently, was in the lead).

Though Grace's guest appearance in the first buddy-heist flick got some chuckles, it was his cameo in the film's sequel — where the actor went ''all Frankie Muniz'' on Rusty (Brad Pitt) after trashing his hotel room — that really scored. And bonus points for that Kabbalah joke.

Who knew the hard-edged, '80s punk rocker was such a hopeless romantic? In the 1998 comedy, Idol helped Robbie (Adam Sandler) woo love interest Julia (Drew Barrymore) while on a flight to Las Vegas.

The legendary mime famously spoke the only word — ''Non!'' — in Mel Brooks' speechless comedy.

When Rodney Dangerfield's rich businessman Thornton Melon was assigned a paper on Kurt Vonnegut's novels, he paid the Slaughterhouse Five author himself to draft the piece. Too bad his efforts were in vain — Vonnegut's paper earned Melon an F, and the following chastisement from his professor: ''Whoever did write this doesn't know the first thing about Kurt Vonnegut.''

The scholar and pop culture theorist helps Alvy Singer (Woody Allen) settle an argument — and break the fourth wall — while Alvy waits in line ahead of a pontificating know-it-all.

Affleck and Damon revisit their humble beginnings in the Kevin Smith-helmed comedy, filming the ill-advised Good Will Hunting 2: Hunting Season with Van Sant once again sitting in the director's chair. We're not sure that ''Applesauce... bitch,'' will catch on quite as quickly as the first film's pomme-related quip.

In the Farrelly Brothers comedy, Cher pulls a Demi and hooks up with a much younger man (boy), played by Frankie Muniz.

The former vice president took time out from saving the world to make a blink-and-you-missed-it appearance on the Tina Fey-helmed show. Too bad that whale was in trouble — we would've liked him to stick around.

He's giving fame one more try: Michael's troubled star got a boost from his cameo in the feel-good ABC comedy, playing the subject of Stone's brain tumor-induced visions. (Prior to Eli Stone, Michael also guest starred as himself in Extras' finale).

The Monkees heartthrob not only agreed to play at Marcia's junior prom, but he also offered himself up as her date. Hmm... think he'd ever heard of those statutory laws?

Tomei may have dated Robert Downey Jr. in the '90s, but according to Seinfeld, the Oscar-winning actress really has a thing for short, stocky bald men — short, stocky, duplicitous bald men, however, don't make the cut (sorry, George!).

Written by Kate Ward, Simon Vozick-Levinson, and Marc Bernardin