Lincoln and his sisters make a bet on who can go the longest without engaging in their most annoying habits.
The Loud children are inside the house on a rainy day doing different things, and Lola is repulsed by Lincoln reading his comic book in his underwear, calling it an annoying habit, but Lincoln is quick to point out that she and the other girls have annoying habits of their own. This gives Lola the idea to call a bet to see who can go the longest without their habits, and if Lincoln loses, he can't ever read in his underwear again, but if the girls lose, they have to buy Lincoln a new pair of underwear he wants to buy. This means that Lincoln can't read comics in his underwear, Lori can't talk to Bobby, Leni can't say "like", Luna can't speak in a British accent, Luan can't tell bad jokes, Lynn can't make everything into a sport, Lucy can't suddenly appear and spook everybody, Lana can't play in the mud, Lola can't look in her hand mirror, Lisa can't do her poop study (or any other "weird studies"), and Lily can't cry.
Leni is the first to lose, as she says "like" after only a second, followed by Lucy when she suddenly appears. As Lola tries to get the girls to stay focused, Lynn is the next to lose, as she can't resist folding laundry and not imagine socks as basketballs. And while Lincoln gets uncomfortable reading fully-clothed, he decides to change his pants and starts to wear Lori's leggings, only to realize that "they really ride up on ya". Luna is tempted to break the bet when she tries to win Mick Swagger tickets over the radio by doing her British accent; she tries whispering into her cellphone, away from her sisters, but she then shouts into it when the announcer can't hear her, causing her to lose.
When Bobby arrives at the house wondering why Lori won't answer his calls, Lola tries to keep Lori from speaking to him, but Lori breaks and lets him in, causing Lana to rush outside into the mud, Lori to congratulate Bobby on their six-week dating anniversary, and Luan to make punchlines out of Lincoln's question for Bobby's lateness. All three lose as a consequence. After Lori goes upstairs to the bathroom (thanks to Bobby giving her the very same milkshake from their first date), Lisa breaks her end of the bet by following her to further her poop study.
With Lincoln and Lola apparently the only two left, Lola tries to make Lincoln, who is now wearing sweatpants, lose by turning up the thermostat to get him to take off the pants. Lincoln sees through her ploy, and he tries to get Lola to lose by cleaning every shiny surface in the living room to get her to see her reflection. Lincoln finally gets Lola to look in a mirror by tempting her to see what she looks like in her uneven makeup; she looks at her reflection in a doorknob, and she immediately bolts upstairs to fix herself, losing her part of the bet. Believing he's won, Lincoln rips off his pants and gloats that he'll now be getting his "victory undies". However, he soon realizes after that he forgot about Lily, and that she hasn't cried once, Lily is declared the winner, and Lincoln can't read in his undies ever again.
Later on, Lola is enjoying herself with her mirror when she sees Lincoln, uncomfortable and miserable reading in his clothes, and she takes pity on him. The next day, Lincoln gets a package in the mail: his victory undies. Lola explains that she bought them for him, saying it's unfair for him to be unable to indulge in his annoying habits while she and the others can indulge in theirs. Lincoln is touched by her generous act, and he proceeds to enjoy his comic in his new undies along with his sisters doing their antics. Outside, Bobby is chasing a chicken in the rain asking about crossing the road.
In the Finnish dub, she is dared to not use a Helsinki slang and speaks actual Swedish, instead of a Swedish accent.
In the Italian dub, she uses a German accent.
In the European Spanish dub, she doesn't use an accent, which isn't mentioned in the episode.
Undie Pressure - The title is a pun on the phrase "under pressure".
Bridal Chorus - Lori's ringtone for Bobby is the well known musical piece Here Comes the Bride, by Richard Wagner.
The end credits for this episode, credit Brian Stepanek as the voice of Dad, despite the character not appearing. Carlos PenaVega is not credited for voicing Bobby.
Lincoln claims reading comic books with his clothes on is uncomfortable, but in "The Sweet Spot", he is shown reading comic books while dressed in the flashbacks, and does not struggle one bit.
When the girls are in a huddle, they can be heard whispering. However, their mouths do not move.
Despite being eliminated, Lincoln never actually read his comic in his underwear. The bet was that Lincoln could not read comics with only his underwear on, but when he got eliminated he still had his shirt on, so he technically shouldn't have been eliminated yet. In addition, he wasn't reading comics, either, therefore, both Lincoln and Lily should've won. However, he got the prize that he wanted.
When Lola was running around screaming to resist seeing her face and hit her head on the chair and fell down, she appears to have front teeth.
In one scene, Luan was taller than Luna.
When Luna tries to win the radio station contest with her British accent, the camera is placed so it looks like the curtain is behind Luna, but when Lincoln and her sisters catch her in the act, the window is behind her, and the curtain is in front of her.
In some scenes, Lola's sash is on the wrong side.
When Lucy pops up and scares everyone after Leni is eliminated, she can be heard saying, "Nice going". But her mouth only shows her saying "Nice".
When Lincoln puts on Lori's leggings, he says the bet wasn't to have to "wear his pants", except he made the bet that he had to keep his clothes on at the start of the bet.
When Luna said, "I bloody love this song", her radio is in her left hand. In the next shot, before Lucy scared her, the radio is in her right hand.
In the Latin American Spanish dub, when Lola shouts, "Forever!", her voice is similar to Lana's.
Lincoln told Luan to give up telling "bad" jokes, and Lisa to give up doing "weird" studies. However, those adjectives are subjective.
The Loud House Underwear Bet Nickelodeon UK
Lincoln Loves His Undies! - Undie Pressure ? The Loud House