Truth-Telling Session

A common form of an Escalating War in a sitcom is when one character lets slip an embarrassing secret about another, and the two start flinging truths back and forth, until a fact comes out that's so humiliating it can't be topped. Sometimes this is capped by a stupid or clueless person accidentally saying something that humiliates themself instead of an enemy.

Sometimes the characters will be telling truths about themselves — generally because they want to show solidarity with someone else whose secret has just come out. This variation inevitably ends with one of them revealing something that, even in this situation, goes miles too far.

One thing clearly demonstrated by these exchanges is that any given sitcom character has more to be ashamed of than everyone you've ever met in real life combined, even if you're Ozzy Osbourne (as can be seen on The Osbournes).

Anime and Manga

 * Subverted in the anime Azumanga Daioh. When the students quiz Nyamo the gym teacher about what sort of student their homeroom teacher Yukari was, Yukari waltzes by humming "love letter" over and over again. This pre-emptive strike causes Nyamo to grudgingly say that Yukari was a normal student. Later on, when rather inebriated, they indulge in a Truth-Telling Session on the streets.

Film

 * 2010: The Year We Make Contact starts with one. The Russian representative who meets with Dr. Floyd at the start simply declares that he's not in the mood to do the usual dance of half-truths and deceptions expected of them when talking to each other and declares that for the next 60 seconds he will only speak the truth, inviting Floyd to do the same.

Literature

 * Justified in Bruce Coville's Magic Shop book The Skull of Truth—a truth-telling session happens around a Thanksgiving dinner table because the family is supernaturally compelled to be truthful.

Live-Action TV
"Inara: You're always breaking the rules, no matter which society you're in! You don't get along with ordinary criminals either, which is why you're constantly getting in trouble! Mal: You think following the rules will buy you a nice life, even if the rules make you a slave."
 * This is particularly popular in Friends. It happened in a Thanksgiving episode, the "Space Mountain story" episode, and the episode where we found out about Chandler's third nipple, amongst others. One time it found an interesting variation by using a temporary love interest as the secret-hearer, and having all the secrets be things that had happened in previous episodes. In an episode where Rachel and Monica pretended to be each other while dating doctors, they began to reveal ugly secrets about each other in the first person ("In high school, I was a cow"; "I use my breasts to get other people's attention." "We both do that!")
 * The exchange in That '70s Show which ended with the revelation that Laurie was born with a tail.
 * In Hey Dude (on Nickelodeon), the four main characters tell each other an embarrassing (but still rather tame) secret about themselves. Naturally, all four of them have spilled the beans before the half hour is up.
 * A weird take on the idea in Mad About You, where the Buchmans wind up shouting their own most embarrassing secrets to a video camera (it's complicated).
 * It goes the other way around in the final episode of Black Books. Manny accidentally blurts out that Bernard's ex-fiancée, whom he has long believed to be dead, in fact faked her death to get out of their marriage, subsequently becoming a very good friend of Fran's; Fran not only didn't tell Bernard that his ex-fiancée was not dead, but in fact informed seemingly everyone else but him that this was the case. The resulting truth-telling slanging match between Bernard and Fran gradually gets turned to smaller and pettier truths, with Bernard eventually winning by pointing out that Fran went to a party that night with a rather daft haircut.
 * Red Dwarf: Gazpacho soup!!
 * That's even better in the book.
 * On How I Met Your Mother, in order to convince Barney to tell a painful story from his past, the rest of the gang tell the most embarrassing stories of their own lives to make it easier for him. Turns out Barney's story isn't humiliating or sad at all (at least from his perspective), he just pretended it was hard for him to talk about so he could get embarrassing stories about everybody else.
 * Also, the episode "Spoiler Alert" has everyone revealing each other's annoying habits, and suddenly they notice them.
 * In the Firefly episode "Shindig", Mal and Inara suddenly end up telling each other what they really think about the choices the other one made.

"Howard: Well, Raj, I just want to say that I'd never betray your trust. Unlike Leonard, I respect you. Leonard: Really? Was it out of respect that you didn't tell Raj about the time you dropped his iPhone in a urinal? Raj: Dude, I put that thing on my face! Sheldon: I think a more amusing violation of Raj's trust is when Howard convinced him that foreigners give presents to Americans on Thanksgiving. Howard: And as long as we're talking about betraying our friends, how about the month Sheldon spent grinding up insects and mixing them into Leonard's food? Sheldon: Excuuuse me, that was not a betrayal. That was an experiment to determine at what concentration food starts tasting... mothy Leonard: You put moths in my food?! Sheldon: For science. Raj: I can't believe you kissed my sister with moth mouth. Leonard: Well, I can't believe you used Sheldon's toothbrush. Sheldon: YOU USED MY TOOTHBRUSH?!"
 * Beside the occasional thanksgiving meals, which are usually more civilized, the Walker family of Brothers and Sisters have a great tendency to involve two or more members of the family revealing dozens or more shameful truths about each other.
 * On The Big Bang Theory, after Leonard confesses to sleeping with Raj's sister (betraying not only Raj's trust but also Howard's, with whom he'd made a pact that they'd never hit on Raj's sister), the following exchange occurs:

"Logan: I never...took matters into my own hands in the boys' locker room after watching cheerleading practice. Duncan: *glares, drinks*"
 * Veronica Mars makes it clear that you never play I Never with friends, or else it can turn into a Truth-Telling Session with booze.

Oral Tradition

 * Anglo-Saxons and other Germanic cultures considered this a noble art form and one of the manly pastimes (Íþróttir, in Icelandic). The Old English name for this contest of wits is a Flytting. It has a prominent place in the epic poem, Beowulf. Also appears in Norse Mythology, in which Loki effortlessly embarrasses every single god in the pantheon.

Theatre

 * The Act I finale of The Addams Family Musical, "Full Disclosure", is one of these gone horribly wrong.

Web Comics

 * This Hellbound webcomic strip has a slight variation on this theme.

Western Animation

 * Happens once on Total Drama Island, but in a rather disappointing turn we don't even get to hear any of them.

Real Life

 * Real life example: This bash quote.