"It's not my BIRTHDAY!!!"So you happen to have a group of friends who want to do something nice to you. What do they do, you say? They decide to make a birthday party for you in the comfort of your own home. When you come home, they all surprise you and tells you happy birthday. Wait. Why are you not happy?! We worked hard to make this party for you! Oh, it's not your birthday? Whoops. This is the trope where characters don't realize that it isn't the character's birthday. This can be played in many ways. Either they forgotten to ask the character when is their birthday, or is because they're just being too kind to the character. This can often be geared towards a grumpy character whom the others want to cheer up. This is the inverse of Forgotten Birthday. This can combine with Scary Surprise Party for extra comedy value. Related to Ironic Birthday, which is when the character doesn't want to celebrate despite the fact it's their birthday. Compare with Birthday Hater for when it is their birthday, but they don't want to celebrate it anyway.
—Squidward, "Opposite Day"
- In The Witch of the Everfree, since Pinkie Pie doesn't know when Sunset Shimmer's birthday actually is, she just takes guesses, leading her to throw Sunset a "birthday" party every month or so.
- In the Steven Spielberg film Always, Pete (Richard Dreyfuss) throws a big shindig for Dorinda (Holly Hunter)'s birthday... except it wasn't her birthday. He keeps saying he remembered it, she keeps saying yeah, but he remembered it wrong.
- Played for deep black comedy with the surprise birthday celebration for Spats Colombo at the convention of the Friends of Italian Opera in Some Like It Hot.
- This is a plot point in Declare: history thinks Kim Philby was born on January 1 but in the book, his real birthday is on December 31, which he hides from everyone because he is functionally invulnerable on all days except his birthday.
- Garrett, P.I.: In Whispering Nickel Idols, Mafia Princess Belinda throws a 60th birthday party for her father Chodo, even though it's not the right day or the right year for it. Everyone she invites already knows this, but come anyway because they realize the party is just a front for a major criminal summit.
- In It's Always Sunny in Philadelphia, the gang plans out a surprise birthday for Charlie to make him feel better. But it isn't his birthday. Frank just said that to trick them into planning a luau party for his own birthday.
- M*A*S*H: In order to brighten the mood of the camp BJ tells everyone it's Hawkeye's birthday and they arrange a Surprise Party for him. Hawkeye 'accidentally" lets slip that the same day is also BJ's wedding anniversary. Ultimately Hawkeye has to go out on a medical emergency so BJ recruits some miscellanous extra to say it's his birthday.
- Inverted in the Seinfeld episode, "The Outing", where George, Kramer, and Elaine each plan on getting Jerry something special for his birthday; Kramer is the first to give Jerry his present, though Jerry insists it's not his birthday, although the others insist that it is, to which Jerry comments, "Maybe you're right, maybe it is my birthday..."
- Daniel gets one of these in the series finale of Stargate SG-1 courtesy of Vala. Played with in that Vala knew full well it wasn't Daniel's birthday, but the crew of the starship he was on did not.
- Just Shoot Me!: Jack wants to get Maya a present for her thirty-fifth birthday, and decides that, after years of neglecting her as a child, he should give her "the gift of me." This makes Maya angry, because her birthday is 7 months from now, and is upset that her own father wouldn't know. Still, Jack is sure that it's someones birthday... and that's when they both realize that they have forgotten Maya's mother's birthday.
- WWE: In one part of the memorable "This Is Your Life" segment on Raw, Mankind brought a clown to sing "happy birthday" to The Rock as well as bringing out a birthday cake for him. Because he was absolutely unimpressed, this is what he has to say to Mankind:
The Rock: "The Rock's birthday is May 2nd, you stupid son of a bitch!"
- Played for Drama in Next To Normal when the ill Diana bakes her son a cake during the song "It's Gonna Be Good"... only for the audience to discover Gabe's been dead for nearly a decade and a half.
- In one pictures for sad children comic, a guy receives a surprise birthday party on the day before his birthday, then on his actual birthday, then on the day after, then on the day after that...
- Played with in Alice in Wonderland. Alice comes upon the Mad Hatter, the March Hare, and the Doormouse celebrating what she thinks is a birthday party, but they're celebrating their unbirthday - which is any day that isn't your birthday. Alice realizes it's her unbirthday too and they include her in the celebration.
- An episode of Fish Hooks had the entire class thinking it was Clamantha's birthday, even though it wasn't.
- On Foster's Home for Imaginary Friends, Bloo keeps throwing surprise birthday parties for Mac, then using them to embarrass him in front of everyone. Of course, to keep Mac from suspecting them, he never does it on Mac's actual birthday...except for that one year when he did. "So basically, I'm never safe!"
- On The Grim Adventures of Billy & Mandy Billy convinces Grim to help him throw a surprise party for Mandy. Grim actually ends up feeling good about preparing for the party. When the two surprise Mandy, she asks Grim if Billy told him that her birthday isn't for several months. Billy says that's what makes it a real "surprise party". Grim breaks down.
- In one Phineas and Ferb episode, Monogram and Carl surprise Perry with a birthday party when he enters his secret lair. Perry's silent stare tells them it's not his birthday. Becomes a Call Back joke later when Perry arrives at Doofenshmirtz's place. Doof mentions he got an invitation to the party but didn't go because he suspected it was a trap.
- In the beginning of the Spongebob Squarepants episode "Opposite Day", Spongebob and Patrick are annoying Squidward by throwing a birthday party for him, which really isn't as the quote from above states it. This is what prompts him to move out of Bikini Bottom, which apparently backfired on him thanks to Spongebob and Patrick.
- Invoked in the Steven Universe episode "So Many Birthdays"—Steven finds out the Crystal Gems don't celebrate birthdays, being ageless, and decides to throw them each a party anyway. They find all of the birthday rituals bizarre or downright terrifying.
- For some reason, Jason Statham's birthday keeps getting referred to as the 12th of September, even though it's actually in July. He usually politely thanks people for the birthday wishes, but also points out it's not his birthday.