After all, that's at least half the fun. This is Scraps, a multiplayer vehicular combat game currently in development for PC. Basically, you build your own cars in it then blast each other (or yourself) apart.
It looks quite fun, judging by the gameplay trailer:
It's one of those pre-alpha proof of concept kind of deals, so one would assume the terrain will look a lot better come release. The core gameplay of goofing around in self-made cars seems to be there and working, for the most part. I'm really digging the song, too.
Scraps: Custom vehicle combat for Windows/Mac/Linux [Kickstarter]