Wiktionary
n. 1 (context comedy English) A popular circus clown routine whereby an implausibly large amount of clowns would climb into or out of a small car. 2 (context industry English) A bait-and-switch car.
Wikipedia
A clown car is a prop in a circus clown routine. A common example of such a routine involves an implausibly large number of clowns emerging from a very small car, to humorous effect. The first performance of this routine was in the Cole Bros. Circus during the 1950s.
The clown car is frequently used as a comedic gag in film. One is featured prominently in Mel Brooks' remake of To Be or Not To Be.
Clown cars can also be used to describe vehicles in computer games that house an unrealistically large number of occupants. They have also been used to describe political contests with a large number of candidates.
Usage examples of "clown car".
This could be a fire truck, an ambulance, a police vehicle, or a clown car.
Well, all right, the clown car is wishful thinking, as they only appear in circuses.
He wouldn't have been greatly surprised if he had glanced at his rearview mirror and seen Thomas Vanadium's blue Studebaker Lark Regal closely tailing him, not the real car raised from Quarry Lake, but a ghostly version, with the filthy-scabby-monkey spirit of the cop at the wheel, an ectoplasmic Naomi at his side, Victoria Bressler and Ichabod and Bartholomew Prosser and Neddy Gnathic in the backseat: the Studebaker packed full of spirits like a bozo-stuffed clown car in a circus, though there would be nothing funny about these revenge-minded spooks when the doors flew open and they came tumbling out.
Get your stuff together, get back in your clown car, and get out of here.
The rest of the crowd followed in the station wagon and when they unloaded, it seemed like a clown car from a circus, an improbably large number of persons climbing forth to stand in the barnyard looking about.