In episode 10 of Ore no Imouto ga Konna ni Kawaii Wake ga Nai!, Kanako Kurusu, one of Kirino's school friends, is tricked by Ayase, another of Kirino's friends, into a cosplay contest, where she wears a Meruru costume that makes her look exactly like the character. Although offstage she gripes about it, while she's performing on the stage, she seems to give herself entirely to the act as she sings and wows the audience. Kanako does such an excellent job that Kirino, who was in the audience, doesn't recognize that its her friend cosplaying as Meruru.
Akira in the Lucky Channel segments of Lucky Star, much to the chagrin of Shiraishi. The funny thing is she's not that old (she's fourteen), but started out as a child star (at three years old!) and has to keep up a Kawaiiko act.
Loony Leo from the comic book Astro City is a strange example. He's a cartoon lion that was accidentally brought to life in the real world. He spends time as a "live-action" actor, a penniless vagabond, a supervillain, and is involved in the death by drug overdose of a 14-year-old girl before he settles down and works in a novelty restaurant. After telling his whole depressing life story to a kid who wants him to do commercials for a car dealership, he scolds the kid for thinking he'd want to do the commercials after all he's been through. Then, at the last minute, he changes his mind, saying "Aw, hell, it's show business, right? Where do I sign?"
Binky the clown from Garfield. He wanted to be an actor originally but they told him he was too short, apparently. So he both loves and hates his clown image.
DC One Million gives us a superhero version: The future Starman hates being a hero, but loves the attention.
Galaxy Quest: Alan Rickman's character, Alexander Dane, was once a serious Shakespearean actor. Ever since having starred in the titular television show, his career has been reduced to appearing at sci-fi conventions and opening electronics stores.
Dane was largely based on Leonard Nimoy, as his show-within-a-show character was a Captain Ersatz of Nimoy's character Spock. Nimoy went through a period of time where he seriously regretted how people only seemed to recognize him as "Spock", using the confusion as inspiration for his book I am not Spock. He later came to terms with it and wrote another book, I Am Spock. While Nimoy was bothered by always being called "Spock", he didn't really hold any contempt for the show or the character.
Another basis was Sir Alec Guinness, a classically trained Shakespearean actor who was outright offended that people only knew him as Obi Wan Kenobi. While he was known for being a consummate professional on and off the set, he didn't respect the films and it was just another job for him.
In the film The Aristocrats, many of the interviewed comedians argue that this is the essence of The Aristocrats joke, since it's about a family that will sink to any depravity to be part of the glamour of showbiz. Sarah Silverman's version of the joke in particular runs thick with this trope.
In the Discworld book Soul Music, when a band shows major promise, and is recruited by Cut Me Own Throat Dibbler, he appoints a somewhat flattened (and smelly) troll named Asphault to carry their equipment. In homage to the joke, he cleaned up after elephants, but they often sat on him. When asked why he didn't leave, Asphault said "Show business is in me soul."
One of the characters commented: "Only sat?" when Asphault described the elephants.
Live Action TV
Johnny Fever in WKRP in Cincinnati starts out like this, but he's not as grouchy after Andy, the new program director, lets him play the music he wants to play (and say "booger".)
House had a character like this in the season 4 episode Live the Dream. The patient of the week was the star on a daytime medical soap but felt ultimately unfulfilled with his job.
This is Andy's entire character arc on Extras (and applies to some of the guest stars/minor characters as well).
A particularly dark example: Mr. Jelly, the ill-tempered, one-handed clown on Psychoville.
Jonathan Coulton's song Bozo's Lament is about a clown who hates and resents his job but doesn't know what else to do. "It sucks to be a clown."
One potential fate of Tex Murphy in the Pandora Directive involves Tex leaving the P.I. business and becoming a clown. Needless to say, his reasons for doing so render him quite jaded.
Sven Bianchi in Questionable Content has a remarkable talent for writing country-western songs that are trite, sappy, and incredibly corny... but also incredibly marketable.
Krusty the Klown on The Simpsons, and his stage name is actually a hint at this. How much it actually applies to him varies Depending on the Writer. Sometimes he's depicted as a hack who's just in it for the money, at other times he laments the crappy material he has to work with. In one episode, he claimed that he'd need a "shoebox full of blow" to go through with producing a particular sketch.
"The Last Temptation Of Krust" plays with both aspects: after noticing his humor is out of step with modern comedy, he quits his job and reinvents himself as an anti-establishment stand-up comedian with great success...then he accepts a huge endorsement from Canyonero SU Vs which causes his new career to tank and him to go back to his old job, which he doesn't mind since he realized his true talent was never comedy... but selling out.
Also from The Simpsons, Reverend Lovejoy after he got Flanderized. That is, after an overly-clingy and needy Flanders got done inadvertently beating the love of his fellow man out of him.
This trope is also the ultimate reason for Sideshow Bob's descent from TV sidekick to homicidal maniac. Bob originally accepted Krusty's offer to be his sidekick because he thought he could both entertain and enlighten the children who would be watching, but his talents were utterly wasted by the lowbrow shenanigans Krusty subjected him to, which in Bob's own words "destroyed more young minds than pinball and syphilis combined!" Finally, Bob snapped and framed Krusty for armed robbery, taking over the show after Krusty was arrested. He immediately turned it into the kind of show he originally wanted to do, one that was educational, entertaining and uplifting all at once...and then Bart Simpson pegged him as the guy who framed Krusty and he went to jail. Suffice to say that it got worse from there.
Miss Carol from an episode of Rugrats behaved like this and Angelica thought her more vulgar version of her TV catch phrase was the real one.
Mother Maggie, a children's TV host from Family Guy, hates children.
Mommy Fortuna in The Last Unicorn. She keeps a dangerous harpy in her circus that she knows will kill her one day, but she doesn't care because she only wants to be remembered, which tormenting an immortal harpy will accomplish. When the unicorn suggests that the harpy be set free, Mommy interjects, "I'd quit show business first!"
Italian singer Cristina d'Avena is said to feel this way, as she does exclusively cartoon theme songs, children shows and nothing else. Publically at least, she claims to be happy with her career.
Marjoe Gortner, an evangelist preacher in the 60's, explained in his documentary that he didn't believe what he preached but loved the attention and money - going so far as to say if he'd had a different background he'd probably have been a rock star.
Despite the public perception that anyone in a mascot/animal/robot costume absolutely hates their job, this tropes is mostly averted by character performers. Many actually love their job and take pride in their level of skill. Especially sports mascots.
There's a very old joke about a man who walks into a bar smelling of filth. He complains to the bartender that he hates his job, cleaning up after the elephants in the circus. He shovels elephant droppings all day long and can't get the smell off of himself no matter how he tries. The bartender asks why he doesn't just quit his job. The man looks back, unbelieving, "And quit show business?!"
Famously averted by Clayton Moore, The Lone Ranger (he loved the role so much his autobiography is called I Was That Masked Man).