Accidental Kidnapping

Accidentally kidnapping someone. This might be What Did I Do Last Night? or Mistaken Identity, or Crime After Crime (possibly started by the first two).

Examples of Accidental Kidnapping include:

Anime and Manga

Inverted in Hayate the Combat Butler. Hayate starts off trying to kidnap someone and ends up rescuing her instead.

Comic Books

Happens in Scare Tactics when Van Zandt steals the Scaremobile. Screamqueen is asleep in her coffin in it at the time.

Film

Alicia Silverstone's character in Excess Baggage. She wants to make her father think she's been kidnapped, so she ties herself up and locks herself in the trunk of a car. Then a real car thief steals the car with her inside...
Happens with a Traffic Warden in Lock, Stock and Two Smoking Barrels.
In The Hangover when the main characters get their car back, they discover that at some point in their "drunken" antics they locked a naked Asian man in their trunk.
Turkish film Varyemez has a rich industrialist getting car-bumped by a bunch of cash-strapped actors. The industrialist, already edgy from the death threats he's been receiving, believes the actors to be kidnappers. The actors just shrug and go with it, hoping they may get some ransom money.

Literature

In Diana Wynne Jones' short story Warlock at the Wheel, the eponymous Warlock steals a car, not realizing there's a girl and her dog in the backseat.
In Timeless, Alexandria's vampire hive kidnaps Alexia's daughter Prudence. Well, they thought they kidnapped Prudence; they got Ivy's daughter by mistake. To be fair, it was two dark-haired toddlers, and Prudence hid under the bed when she heard them break in.

Live Action TV

Happens in various fashions at multiple points in It's Always Sunny in Philadelphia:
- The straightest example of this trope would be, after a critic writes a bad review of Paddy's calling it "Paddy's Pub: The Worst Bar In Philadelphia" (the episode's title), Charlie gets drunk and kidnaps him, leaving the rest of the episode has an exercise on how to release him without legal repercussions.
- In "The Gang Gets Extreme: Home Makeover Edition", the gang kidnaps a family in a misguided attempt to remodel their house. After destroying their house instead, they have to give Dee's newly-acquired house to the family in compensation.
- In "The Gang Exploits the Mortgage Crisis", Frank forces the kids of the family resident in the house he just bought to do work in the basement when their parents are at work. Same ending as the last one.
In season 1 of Arrested Development, Michael gives a Mexican woman a ride thinking that she's his mother's housekeeper, Lupe. She was not. This woman is then disturbed to see red splatter all over the front seat (actually nail polish spilled by Michael's sister), and shovels and a human skeleton in the back (actually taken from an excavation site by Michael's brother). Michael wants to prove that he's a good person by giving this woman a ride, refusing to let her out "too soon" when she becomes distressed by the shovels and "blood spray". She eventually runs away when he stops in the Wetlands, and the episode ends with Michael being arrested.
In the MacGyver episode "Hearts of Steel", kidnappers accidentally kidnap the housekeeper's daughter rather than the daughter of a business magnate because the two girls have swapped jackets.
Happened in The Bill': A guy carjacked a car and didn't realise there was a baby in the back. The baby was found injured and It turned out that she'd been hit by her dad just beforehand.
Happens in The Office, when Michael holds the pizza boy hostage and demands a better deal, and his coworkers inform him he is committing a felony by holding a minor against his will.
It happens on The Nanny, when Fran takes a baby from an ethnic woman who had her hands full on a subway. Fran and Maxwell considered caring for it until they see a criminal sketch for Fran on TV.
In Titus (sit back, cause this is complicated), Tommy's ex-girlfriend came back to town and he wanted to talk with her, only he was limited by a past restraining order. He ran into her car and then in a note claimed that Titus would repair her car for free (owning his own car shop). When she came in Tommy tried to hide, but she ended up seeing him. Panicking, she barricaded herself in Titus' office and tried to call the police, but Dave yanked out the phone line. Titus does a Face Palm and declares that they now have a hostage.
Played straight in the finale of Dark Angel. Max and the gang are surrounded by their foes while at work, forcing them to take their collegues hostage.
Better Off Ted:
- In one episode, Linda is inadvertently drugged and, in a misguided fit of appreciation, steals a baby so she can claim it as her own by writing her name on it.
- In another episode, Ted regales the demographic he's unpopular with with a tale of how, in his youth, he once accidentally kidnapped a random pig rather than another school's mascot.
Happens in Pushing Daisies during a flashback to Olive Snook's childhood. When a pair of men burglarize her home, she stows away in their getaway car to escape her neglectful parents, and she and her kidnappers have a wonderful time together. (Her parents are so neglectful that they don't notice her absence until the accidental kidnappers berate them for failing to look out for their daughter.)
In the My Name Is Earl episode Very Bad Things Joy steals a delivery truck without realizing that there was a delivery boy still inside. Earl and Joy then have to figure out how to release him without getting caught. In the end of season 2, Joy goes to trial and Earl ends up taking the rap for her and going to jail.
Early in Burn Notice, Mike gets kidnapped during a bank heist. So a few seasons later when he calls to say he's involved in a hostage situation, everyone assumed he got kidnapped again.

Mike: Actually...we're the hostage takers. It's a long story.

Real Life

Walt Disney once technically kidnapped then-Vice President Richard Nixon by taking him for a ride on the Disneyland Monorail before Nixon's Secret Service entourage had a chance to board the vehicle.

Western Animation

The King of the Hill episode "Lupe's Revenge", where on a field trip to Mexico, Peggy accidentally brings along a local girl, and is arrested for kidnapping when trying to bring her back.
On The Flintstones, Dino goes missing and Fred brings back what he thinks is Dino, but he was really taking someone else's ~~dog~~ snorkasaur from its own yard.
Done in Avatar: The Last Airbender, in "Return to Omashu". The gang lead some freedom fighters out of the city, and accidentally get the Fire Nation Govenor's son as well. He was just following the Team Pet.
In The Nightmare Before Christmas, Jack orders Lock, Shock, and Barrel to kidnap Santa Claus. However, on their first try, they somehow manage to kidnap the Easter Bunny by mistake, much to Jack's chagrin.