Some kids are playing the "get him with the door" game, where they open a car door and tap the rear tire of a bicyclist they are passing. The cyclist is on the left of the street, so they are driving down the left center of the road to tap the bike.
As the kid in the back seat taps the bike, he loses his balance and ends up hanging out the back door, laying horizontally. The car then goes past a parked car, and the bumper catches the kid under the chin/upper chest area,
pulling him out of the car.
As kids do today, they were taping this game on a camcorder. If you want some real laughs, travel some websites for clips, people have:
1 shot each other with bottle rockets
2 shot their girlfriends with paintballs
3 set themselves on fire numerous times...seemingly without any real skills
at firefighting
4 set up fights, without any real fighting skills
5 "curbed" each other
6 taped fights of people with very real fighting skills
and any number of strange things they decided to do at the time.
Anyway, I've only seen this clip on windows player.