Flash Mob Coverup

This trope describes situations where a character sets up a flash mob or similar situation for the express purpose of obscuring or otherwise facilitating a separate, secret purposes. This is often, though not exclusively, for criminal reasons.

Examples of Flash Mob Coverup include:

Film

Tim Burton's Batman: Joker appears among some mimes in order to perform a murder with a deadly quill pen, and he arranges a parade with balloons full of poisonous Smilex gas.
Subverted in Quick Change. A man dressed as a clown robs a bank and takes hostages. The police chief thinks the man will dress some of the hostages as clowns and then try to escape in the middle of them, making it impossible for the police to tell which one is him. Instead he changes into civilian clothes and escapes by pretending to be one of the hostages.
The remake of The Thomas Crown Affair with Pierce Brosnan has Thomas Crown, inspired by the painting The Son of Man, dressed in suit and Bowler hat escaping by arranging several other men in the same outfit appearing.
St Trinian's 2: The Legend of Fritton's Gold has the girls of the school arrange for a flash mob to provide a distraction so that they can evade the bad guy's surveillance.

Literature

Little Brother, by Cory Doctorow, provides an example of this; the Xnet was used to set up an event based on a vampire LARP in order to provide cover for Marcus and Ange to meet up with a DHS mole.

Live Action TV

In one episode of Castle, a kidnapper requires a ransom payment in a specific make of backpack. When the drop is made, the cops take down a man with that style of backpack, only to find that this trope was in effect.
Subverted in an episode of CSI: Miami. It appears a Flash Mob was used as a cover for a murder (or to dump the body), however it turns out someone who didn't want to report the body (because they didn't want to implicate a friend) but didn't want to just leave it there arranged the flash mob so someone would find it.
An episode of CSI New York, however, played it straight: in "To What End?", a killer who commits a murder while dressed as a clown covers his escape by placing an ad on the internet calling for people to show up on a particular street at a particular time.
One of the creatures in Grimm formed flash mobs via text and Twitter to cover up a series of murders committed via bee-sting overdose.
Two examples from Leverage:
- The season one finale has the team handing out copies of the "little naked dude" statues they're allegedly trying to steal in order to throw off Sterling and his men.
- Another example in Season 4: In The Radio Job, Nate's father manages to escape by calling up a radio and saying that he will drop a million dollars from the roof of the patent office because he is sick of inventions being stolen, causing dozens of people to crowd the exit and hide him as he runs away from the crew. Explicitly stated in-universe as well, as Nate says the man called up his own flash mob to evade capture.
Episode "18-5-4" of The Mentalist possesses a similar plot: the killer places an audition notice for clowns who must arrive in full costume, then commits the murder while dressed as a clown. Bonus Points: the victim had a fear of clowns.
In the Numb3rs episode Animal Rites, the villain organized a flashmob ahead of time to distract the authorities at a key moment.

Real Life

A man placed an ad on Craigslist offering landscaping work, instructing applicants to be at a certain intersection at a certain time, wearing "Yellow vest, safety goggles, a respirator mask...and, if possible, a blue shirt". About a dozen men showed up, and it caused some confusion when a bank at that intersection was robbed by the man wearing that exact outfit. The robber himself used an inner tube to float down a nearby creek. He was caught a few weeks later.