"Walk On the Wild Side" Episode

In most sitcoms there is always the one character who is responsible and trustworthy. They are structured, neat and orderly and would never think of doing anything illegal. They might be a Control Freak but they don't have to be.

If this character exists in the series then 9 times out of 10 there's going to be an episode where one of the other characters tells them they need to "lighten up" or "cut loose". Our responsible character will start to worry that they are too boring and so will eventually get wild and spontaneous.

It's almost a given that they will go overboard and something akin to We Want Our Jerk Back happens where the rest of the characters realise they do need some order and discipline in their lives, which the responsible one provided. They'll be back to being responsible by the end of the episode and they'll either reveal how much they hated being spontaneous or resolve to be a bit more fun without going overboard.

If it's the latter then expect this to be forgotten by the next episode. This will almost always happen to a female character but male examples aren't unheard of as well.

Film

 * Used as a bit of a joke in the film of Harry Potter and the Order of the Phoenix, where Hermione remarks that it's fun breaking the rules. It's worth noting that in the book, it is Hermione's idea to start up an illegal Defence Against The Dark Arts society which could technically count as an example of the trope.

Literature

 * Terry Pratchett's Discworld novel Making Money has an example that gives a Shout-Out to the Twelfth Night example below: the austere and humourless bank clerk Mavolio Bent, a man who ran away from the circus to join a bank, suddenly re-asserts his destiny and heritage as a circus clown.

Live Action TV
"Kirsten: You know what, I was supposed to call the man about the invitations today. And you know what? I didn't. (claps hands) What the hell!"
 * In a two-part episode of WKRP in Cincinnati Disc Jockey Dr. Johnny Fever falls into an alter-ego (Rip Tide) a shallow host of a Disco-themed t.v. show. This provides him with more fame and a larger fanbase but it also causes him to give into his urge to exploit his fame to satisfy his basest desires.
 * In the Season two Episode A Many Splendored Thing of the show Homicide: Life on the Street uptight detective Tim Bayliss investigates a murder that involved participants of an SM sex club. The end of the episode finds him having purchased a kinky-looking jacket strolling along Baltimore's infamous sex strip "The Block"
 * Monica in Friends got two examples of this.
 * One was a minor subplot where the other friends suggest she not get so uptight about things like coasters and leaving her shoes out of her room. The end of that episode has a Crowning Moment of Funny where she can't sleep because she's worrying about leaving the aforementioned shoes. She gets to considering putting them in her closet and getting up early to put them back out before she realises "you need help" and goes to sleep.
 * Another episode had someone stealing her credit card. When Monica tracked the woman down, she found said woman a lot of fun and started doing everything with her to the point where she was drunk in the middle of the day and kept missing work.
 * In What I Like About You Jeff says to Val he wishes she was more spontaneous. She goes a bit wild during the episode but reveals at the end the whole experience "nearly killed me".
 * In Sabrina the Teenage Witch Zelda temporarily moves in with Sabrina and her college roommates and decides to become a "hang-loose gal" which involves eating the entire contents of the fridge, spending all night at a rave, driving around in a van with a guy named Vick and trying to get a tattoo. In this case it's resolved by Zelda's subconscious stopping her from doing something untrue to herself.
 * In Lizzie McGuire, Lizzie bonds with a bad girl in detention and starts going bad herself until her friends convince her she's a good girl at heart with a terribly made documentary.
 * Party of Five:
 * In the third episode, straight-A student and bookworm Julia convinces her friend to start going to parties during the week. The friend eventually has enough and disappears from the show but Julia keeps on with this new lifestyle and her grades start slipping. Her brothers try to convince her to go back to her goodie-two-shoes persona but she eventually finds a balance.
 * Pops up as a joke in the second season where Charlie tells Kirsten she's a lot like her mother, prompting her to fret that she doesn't always make plans.


 * Parodied in an episode of Scrubs where Elliott decides to go out on the town for the night. She steps out of a taxi and her hat is immediately stolen. She jumps right back into the taxi and screams "get me out of here".
 * Malcolm in the Middle has Malcolm turning his brain off for one episode in an attempt to get with a ditzy girl. It works fine until he gets into a situation where his brain would have come in handy.
 * In The Brothers Garcia Larry gets sick of being called a goodie two shoes and tries to throw a Wild Teen Party that predictably gets out of control.
 * Several Star Trek episodes based on the holo-deck could qualify for this.
 * Wings provided the "Joe Blows" two-parter. Part 1 sees Joe so overwhelmed by being taken advantage of or constantly annoyed from all sides. So after thirty-five years of being the most responsible person on Nantucket, he finally loses it, gives an epic "The Reason You Suck" Speech and then steals Lowell's motorcycle to get away. By the time we catch up with him in Part 2, he's now partying and living it up in bars along the coast. He's basically become like Brian, who is now trying to keep the airline afloat and be the responsible brother.
 * The How I Met Your Mother episode "The Pineapple Incident" has the gang convince Ted to drink instead of think. He wakes up next morning with a sprained ankle, burned coat, several drunken messages on Robin's phone and a girl he's never met before in bed next to him. Oh and a pineapple that we never find out where it came from.
 * On Buffy the Vampire Slayer, Willow gets a little fed up with her reputation as Old Reliable and flirts with danger a bit by doing a dark incantation with Anya. It doesn't end very well.

Theater

 * As old as Shakespeare: in Twelfth Night, the rigid Puritan Malvolio lets it all hang out by dressing in flamboyant fashions meant for somebody twenty years younger and protests his love for his shocked female employer.

Western Animation

 * There was an episode of X-Men: Evolution titled "Walk On The Wild Side" that played with this trope. It involved all the X-girls and Boom-Boom forming a vigilante crime fighting group, even Jean who was the responsible one.
 * Susie in All Grown Up! gets told she's too perfect by the popular girls and decides to go bad for the episode. Angelica of all people tells her to calm down.
 * In As Told by Ginger Ginger gets fed up of being called a nice girl and crashes a high school party. This leads to a rumour getting started about her and a bad boy called Jake. Ginger realises she preferred being known as a nice girl.
 * SpongeBob SquarePants has an episode where Squidward gets so fed up with Spongebob and Patrick's antics that he decides to move out into a gated community filled with other squids who share his interests. Inside, he finds that everyone else has a Easter Island head house, everyone else loves playing the clarinet, everyone else loves riding their paddlebikes, everyone else loves ballet dancing, and everyone else enjoys eating canned bread. He's thrilled at this, but soon gets bored of the same routine every day, to the point where he starts going out of control and just lets loose while playing around with a leaf blower. The other citizens filled a formal list of complaints, but Squidward tells them off by flying his leaf blower into the sky while screaming wildly.
 * Avatar: The Last Airbender: Katara decides to pull a scam with Toph to prove she can be fun. It backfires, horribly.
 * In The Simpsons:
 * This happens to Marge on many occasions, ranging from running from the law with her friend after stealing her ex's car, taking part in a monster truck rally and gaining road rage from a Canyonero. Driving seems to be her recurring Berserk Button.
 * In another episode, Lisa becomes a delinquent after getting "Homemaker" in an Inept Aptitude Test and being told that she'll never become a professional Jazz musician due to her stubby fingers. This culminates with her committing an expulsion worthy offense (stealing all of the teachers' guides) to which Bart takes the fall, not wanting her to ruin her life.

Other

 * When a middle aged man does this it's sometimes said that they're going through a "Midlife crisis".