This can have one of two main variations:
- Carol also has feelings for Bob and is overjoyed, Bob now has to find some way to convince her it was all a mistake.
- Alice just saw what happened and is likely to not be pleased.
In the worst case, BOTH of these things happen. Once in a blue moon, it dawns on Bob that Carol really is much better for him than Alice.
Usually played for comedy, but occasionally for drama. Compare: Love Letter Lunacy (which is mainly a specific variant caused by problems with the postal service). See also Accidental Hand Hold and, more severely, Accidental Marriage.
- Love Hina: Keitaro wants to finally admit his feelings to Naru and asks her to meet him at the old building near the Hinata Inn, which is said to grant happiness to those that declare their love there. He hears her approaching and embraces the person from behind, admitting that he loves her...! And ends up getting his adopted sister. Who is ecstatic that he loves her. The next chapters revolve around Keitaro explaining the mistake, and trying to confess to Naru again.
- School Rumble: This is how Harima and Eri start off their relationship, as Harima mistakenly confesses to Eri instead of Tenma. Although Eri hadn't had any feelings for him before that, his heartfelt confession—in contrast to all the shallow confessions she got from the other boys and easily brushed off—freezes her into embarrassed panic. Harima is likewise frozen in panic when he realizes what happened.
- Potemayo also has an example, when one of Those Two Guys "practices" confessing to one of the Moe Blobs only to do so right in front of another girl...
- How Ataru of Urusei Yatsura ended up with Lum. Also a case of Accidental Marriage.
- And a similar thing happened in To Love-Ru, with someone (usually Lala) getting in Rito's way every time he tries to confess to Haruna.
- Ranma ½':
- Ryoga finally worked up the nerve to tell Akane how he felt and why he'd used a love-inducing artifact — he'd meant it for her, and hit Ranma instead. But his declaration was also accidentally given to Ranma, who didn't take it well.
- In one arc, Ranma and Nabiki become engaged, instead of Ranma and Akane. After Ranma finds out that Nabiki's been playing him this whole time for a profit by saying she loved him, he wants revenge. So, he decides he'll make her feel weirded out by pretending to be in love with her. He invites her on a date, and eventually, Nabiki ends up being chased by Ranma in a maze. Ranma's determined to see it through, so he pulls her through a hedge and screams that he loves her. To his great distress, it turns out to be Akane, not Nabiki, in his arms. Cue major freak out. (This example is possibly inverted in that he wanted to tell the non-love interest, not the love interest, that he loved her.)
- In Swan Lake and its ballet adaptation, Siegfried is tricked into doing this by Rothbart when he disguises his daughter Odile as Odette, his true love. Having thus broken his vow of love to Odette, she no longer has a chance to escape the curse that forces her to live her daylight existence as a swan. Worse, Odette (in swan form) helplessly watches this from outside the castle. In the animated version The Swan Princess, this is enough to nearly kill her.
- A deleted scene of Star Trek (2009) depicted Kirk apologizing to an Orion woman about getting her in trouble, only to find that he's talking to a different Orion woman.
- Dinner for Schmucks has a variation in which the main character (Tim) is very well aware that the girl he's proposing to is not his (at this point ex-) girlfriend Julie, but is forced to pretend she is in order to avoid disrupting The Masquerade. Both types come into play: the girl is a former one-night-stand of Tim's who is delighted about the proposal, and Julie walks in just in time to see it.
- From The Swan Princess, Derek makes a vow of everlasting love to who he thinks is Odette, but is actually Rothbart's henchwoman in disguise. That vow was the only way Derek could free Odette from Rothbart's spell that turns her into a swan during the day, and when he makes it to the wrong woman, it dooms Odette to die. Made more painful in that the real Odette, in swan-form, is just outside the window and trying to get his attention from making the mistake.
- P. G. Wodehouse's Jeeves and Wooster: Bertie Wooster made a declaration of love to Madeleine Bassett on behalf of his friend Gussie. She took it as coming from him and forever after would decide to marry Bertie and make him happy whenever her love life went awry.
- In Jill Mansell's novel Millie's Fling this occurs. Hugh decides to tell Millie he loves her, however, when he proposes to "her" she is dressed in her gorilla suit and it turns out to be her best friend - because the stripper was too busy to fill in for Millie and the history teacher wouldn't fit in the costume. It turns out Millie is in London watching her friend the recently divorced novelist have sex with her arch-enemy in a toilet cubicle. It Makes Sense in Context. However, the best friend is uninterested in Hugh and is evilly amused - and then proceeds to tell everyone she knows.
- Vita Nuova: People mistake Dante's longing poems for a declaration of love to an attractive woman that the poet doesn't really know that well. He's actually quite happy with the mistake, since it means no one will know who he really is in love with and he can continue with his writing without drawing suspicion.
- An episode from a later season of Coupling reveals that Patrick actually wanted to get Sally's number and ask her out, not Susan, Sally's best friend, whom he winds up dating until the very first episode of the season.
- On Gossip Girl Serena gives her mask to Jenny at the Masquerade, causing Nate to confess his love for SERENA to Jenny. Blair, his girlfriend at the time, dumps him when she finds out, and Serena didn't recognize his true feelings until much later.
- In Friends, during Ross's wedding to Emily, he accidentally says "I take thee Rachel" as his bride instead of Emily's name. Emily wasn't very happy.
- Higgins, of Magnum, P.I. has to break the news of his intention of marrying another woman to his gal pal Agatha - and handles it so badly she thinks he's proposing to her. Ouch.
- In Final Fantasy IX, Eiko writes Zidane a love letter, and drops it off where Zidane will find it. Steiner finds it instead, and assumes it's a love note to him from Beatrix. He drops the letter, causing Beatrix to find it, who assumes the inverse.
- In WarioWare: Smooth Moves, a football player works up the courage to admit his love to Mona (who passes by him... twice) only to explode on a stray cheerleader.
- Defied in It's Walky!. Danny meets with his ex, Sal, with whom there is still a mutual attraction. Danny, however, has moved on and is now in a stable relationship with Billie. He informs Sal that he intends to propose to Billie soon, and Sal congratulates him and asks to see the ring. Danny refuses, saying he knows how this goes; "I pull out the ring, and Billie comes walking around the corner..."
- Road Rovers: The Rover's plane is about to crash, and Blitz grabs the hand next to him and declares his love for Colleen. The hand was Exile's. His response?
Exile: "Please consider therapy."
- Phineas and Ferb has a comical example. Phineas asks Isabella if she's ready to take the next step in reference to the day's project. She starts gushing and telling him that she's been waiting for him to ask her all this time until she realizes what it was he was actually talking about. Naturally, she changes the subject by asking where Perry is.