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Neil Patrick Harris in 'Harold & Kumar Go to White Castle' (2004) -

Harris makes his first appearance high on ecstasy, as he begs Harold and Kumar for a ride. He then goes on to steal their car. In real life, Harris is a happily married man with two children, and no ecstasy habit!

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Nicolas Cage in 'The Unbearable Weight of Massive Talent' (2022) -

In this movie, Cage plays an even more over-the-top version of himself, who, in need of money, agrees to attend a fan's birthday party. The problem is, that fan (played by Pedro Pascal) is wanted by the CIA for an alleged kidnapping.

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John Malkovich in 'Being John Malkovich' (1999) -

A puppeteer (played by John Cusack) finds a portal into the brain of actor John Malkovich, played by none other than Malkovich himself. Anyone who enters the portal can take over Malkovich's body, but when Malkovich crawls in there himself, things get a little weird.

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Debra Messing in 'Bros' (2022) -

Messing plays herself as a potential sponsor for the LGBTQ+ museum the film's lead character, Bobby Lieber (Billy Eichner) is trying to open. Clearly joking about her time on 'Will & Grace,' she freaks out when Bobby tries to talk to her about his personal life, and she affirms that she's not her character Grace. 

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Colin Firth in 'Rye Lane' (2023) -

While he doesn't play the "real" Firth, the characters in this rom-com make it a point to call him Colin, and the name of his place of employment, Love Guac'tually, is a clear nod to Firth's holiday classic 'Love Actually' (2003). 

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David Bowie in 'Zoolander' (2001) -

Bowie only appeared in one scene of 'Zoolander' (2001), but he still played an important role. He judged a walk-off between the two main characters. Ben Stiller, the film's star, writer, and director, called working with the rock star "a high point in my career."

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Al Pacino in 'Jack and Jill' (2011) -

Known as one of the toughest guys in Hollywood, Pacino gives us a different side of himself as he falls in love with Jill, played by Adam Sandler. He also gets a good jab in at his own expense, when he makes fun of his lone Oscar win.

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Bill Murray in 'Zombieland' (2009) -

In one of the funniest and most unexpected cameos, Murray stars as himself as one of the lone survivors in a zombie apocalypse. 

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Justin Bieber in 'Zoolander 2' (2016) -

The sequel to 'Zoolander' (2001) is just as full of celebrity cameos as the first one. In this one, we get to see Bieber as a secret agent version of himself.

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Margot Robbie 'The Big Short' (2015) -

'The Big Short' (2015) which details the events leading up to 2008's financial crisis, features a number of complex financial terms and situations. Robbie's scene is her in a bubble bath drinking champagne, and explaining what exactly the mortgage crisis was. 

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Selena Gomez in 'The Big Short' (2015) -

Gomez also appears as herself in 'The Big Short' (2015) but at a blackjack table next to Nobel Prize-winning economist Richard Thaler. She explains what a synthetic CDO is, by using the simple metaphor of a blackjack game.

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Keanu Reeves in 'Always Be My Maybe' (2019) -

When it's revealed that John Wick himself is Sasha's (Ali Wong) new boyfriend, it's understandable why her best friend Marcus (Randall Park) would be a bit shocked. 

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Tobey Maguire in 'Tropic Thunder' (2008) -

'Tropic Thunder' (2008) is about a group of actors who get stranded in Vietnam while filming a war epic. When establishing the careers of each actor, they all get a fake trailer of a movie that they starred in. Robert Downey, Jr.'s character, Kirk Lazarus, stars in 'Satan's Alley,' a melodramatic romance between two monks. One of the monks is Lazarus, and the other is Maguire.

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Eminem in 'The Interview' (2014) -

Eminem was interviewed in 'The Interview' (2014) and he nonchalantly came out as gay, which is probably in response to accusations of his homophobia. An already controversial movie, Eminem makes fun of his public persona. 

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Joaquin Phoenix in 'I'm Still Here' (2010) -

Directed by Casey Affleck, the Oscar winner plays a scraggly-bearded, rapper-from-hell reinvention of himself. The movie is supposed to be a satire of the relationship between celebrity and the media.

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Michael Cera in 'This Is the End' (2013) -

'This Is the End' (2013) depicts what would happen to a bunch of Hollywood stars during the apocalypse, and Cera plays a hilarious cocaine-fueled monster. 

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Seth Rogen and James Franco in 'This Is the End' (2013) -

Also in Judd Apatow's comedy horror, Rogen and Franco's fictionalized versions have to dodge everything from sinkholes to demonic possession.

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Tom Cruise in 'Austin Powers in Goldmember' (2002) -

Cruise appears in the final 'Austin Powers' movie, which, as usual, parodies multiple 'James Bond' movies. He appears in a movie-within-a-movie, as he plays himself playing Powers.

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Arnold Schwarzenegger in 'Last Action Hero' (1993) -

Schwarzenegger plays an invincible, but entirely fictional, LAPD cop whose movie world bubble gets burst by a teenage moviegoer propelled into the screen. But then the pair travel back into the real world to save the real Schwarzenegger from being assassinated at the premiere of the film they've just escaped from. 

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Ben Affleck and Matt Damon in 'Jay and Silent Bob Strike Back' (2001) -

In 'Jay and Silent Bob Strike Back' (2001), the main characters, Jay and Silent Bob wander onto the set of 'Good Will Hunting 2: Hunting Season,' where they meet Affleck and Damon.

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Bob Barker in 'Happy Gilmore' (1996) -

In 'Happy Gilmore' (1996), Adam Sandler's character is a hopeful hockey player who discovers he has a talent for golf. When he qualifies for a professional-amateur tournament, he's partnered with 'The Price Is Right' host Bob Barker, who gets overly competitive. 

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Howard Stern in 'Private Parts' (1997) -

'Private Parts' (1997) is an adaptation of the autobiographical 1993 book of the same name by radio personality Howard Stern. And of course, he played himself! 

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Megan Fox in 'The Dictator' (2012) -

In this political satire, where Sacha Baron Cohen plays fictional dictator General Aladeen, the 'Jennifer's Body' (2009) star plays as herself. 

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Jean-Claude Van Damme in 'JCVD' (2008) -

The "Muscles from Brussels" surprised everyone when he played a self-pitying version of himself, even rejected by his own daughter. Van Damme also gets to briefly show off his martial arts skill!

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William Shatner in 'Free Enterprise' (1998) -

In this rom-com, two self-proclaimed geeks are each experiencing midlife crises, until they come across 'Star Trek' legend Shatner in a bookstore. Shatner plays an exaggerated version of himself. 

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Paul Giamatti in 'Cold Souls' (2009) -

In an existential and surrealist comedy-drama, Giamatti plays an actor named Paul Giamatti who has trouble preparing for the title role in Chekhov's 'Uncle Vanya.'

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Ryan Seacrest in 'Knocked Up' (2007) -

In 'Knocked Up' (2007), a movie about a one-night stand between a career driven woman and a slacker, Seacrest pokes fun at his TV persona by dropping a lot of f-bombs. In the movie he also claims to be more famous than the celebrities he interviews.

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Steve Coogan in 'Tristram Shandy: A Cock And Bull Story' (2005) -

Steve Coogan appears to like playing Steve Coogan. He's done so in 'Coffee and Cigarettes' (2003),  'Darkwood Manor' (2011), and the food-tour sitcom 'The Trip.' 'A Cock and Bull Story' (2005) also saw Coogan first team up with his 'The Trip' co-star Rob Brydon and director Michael Winterbottom for another heavily improvised tale. 

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Bruce Campbell in 'My Name Is Bruce' (2008) -

A horror comedy, the cult filmmaker favorite produced, directed, and starred in this tale. Campbell stars as a washed-up B-movie star tasked with saving a mining town from an evil force by fans who can't separate fact from fiction.

Sources: (Insider) (Time) (Mental Floss) 

See also: Movies that led actors to quit the film industry

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