Put explosions and decent physics in a game and you can be sure people will spend a lot of time making some very impressive things blow up. In this case, over 100 cars at a time, in what we can call a fiery display of metal-and-upholstery fireworks.
If you're wondering how it was done, creator SubParButInHD didn't do things the hard way by parking each car individually. Instead, he used a car spawning cheat to line stuff up, dropped some sticky bombs, got to a safe distance then broke out the popcorn.
GTA V - Massive chain reaction explosions (100+ cars) [YouTube] Chain Reaction [imgur]