Lots of things can happen at a Slumber Party...Wild Teen Partying, a Childish Pillow Fight or a Fanservice Faux Fight, gossiping and chit-chatting, and passing (or failing) of The Bechdel Test... and then there's this trope.
A character reveals that the slumber party she (and usually, it is she) is attending or hosting is the first sleepover she has ever been to. Usually, they happen to be at least in their early teens or even older, and are at an age where most of their peers have already been to sleepovers. This trope is used to establish them as socially awkward.
The trope is usually the result of several things: The kid whose first sleepover it is is a nerdy bookworm type, or perhaps she has overprotective parents who sheltered her from other kids to a fault. Or s/he might be perceived as a loser by the more popular crowd.
Either way, the kid whose first sleepover it is will typically feel nervous about committing a faux pas. If they are hosting the party, expect them to be overly worried about everything being perfect. If there is a person they don't know at the party, expect them to be nervous about making a good impression.
- In Cavewoman: It's a Girl's Life, Carrie decides to throw a Slumber Party for Meriem and Mona after learning that Meriem had never been to one (having spent her teen years in the jungle). Mona, who had a very sheltered upbringing, finds it quite awkward at first, as Carrie throws a slumber party that is much more 'adult' than she was expecting.
- One episode of Ally McBeal sees Ally fretting over her daughter Maddie's first sleepover, owing to her own bad experiences with other girls when she was growing up.
- A rare male example happens in Atypical; Sam has a sleepover at his friend Zahid's house in preparation for going to college (Sam is autistic and has never spent the night away from home before). The various noises and sounds in Zahid's room irritate Sam and make him leave the room, and a police officer notices Sam wandering down the sidewalk. A misunderstanding causes the officer to think Sam is on drugs, and Sam and Zahid are taken to the police station. At the station, Zahid notices the clock displaying 12:07, and he points out to Sam that Sam's managed to stay away from home past midnight.
- Amy in The Big Bang Theory is excited to have her first slumber party at Penny's with Penny and Bernadette. She's in her thirties and Penny and Bernadette pity her as she had no friends prior to meeting her boyfriend Sheldon and his social group. She's very awkward about the whole sleepover, e.g. she thinks girl talk is talking about female anatomy, she wants to play all the games (like truth or dare) and even tries to make a pass at Penny off-screen, claiming her internet sources list lesbian experience as a vital part of sleepovers.
- One episode of Cold Case revolves around a first sleepover gone wrong - the newcomer was only invited so that the other girls could humiliate her, and when she wouldn't play along, one of the other girls accidentally killed her in a blind rage, afraid that she would become the new designated loser in the group.
- In The Troop, awkward geek Felix shows up in drag to crash the slumber party thrown by Hayley because there's a monster they have to hunt, but he has such a good time, and is actually accepted by the girls more in his "Felice" persona that he goes racing back to the party after they've defeated the monster.
- Arthur: Jenna is invited to Muffy's sleepover, and she is worried because she wets the bed.
- Bob's Burgers : In the season four episode "Slumber Party", Louise is forced into having her first sleepover by her doting mother Linda, who proceeds to invite only girls Louise can't stand. Louise manages to drive away Jodie by claiming Linda is fighting off an illness, and scares Harley and Abby off by claiming Gene has a crazy, deformed twin brother who lives in the basement, but the seemingly bland and ordinary Jessica proves to be a tougher nut to crack.
- In the My Little Pony: Friendship Is Magic episode "Look Before You Sleep", Rarity and Applejack have to spend the night with Twilight Sparkle due to a big rainstorm. Twilight uses this as an opportunity to hold her very first sleepover, since she never had one, and therefore is literally by-the-book as she uses a guide on slumber parties to move the plot along. The slumber party gets gradually ruined as Applejack and Rarity had been in an argument and are still mad at each other during the sleepover.