In the grim darkness of the future, there is only smash up derby.
Destructicus Prime is a miniatures smash-up derby game that was born when Feng observed that the funnest part of Warhammer 40k was blowing vehicles up.
Basically, you set up an arena on a large table. The arena can include barriers, gates, ramps, bombs, and anything else you can come up with. Players bring toy vehicles of approximately the same scale. These can include models from miniature wargames (like 40k), matchbox toys, animals and monsters such as riding dragons or toy dinosaurs, and so on. Players then race these vehicles around the table trying to score points while creating as much destruction and mayhem as possible.
Making shooting sounds and explosion noises while doing this is recommended.
Since its inception the game has been through five revisions, and the final version plays quite well. I've posted the Destructicus Prime rules on my Web site.
The one thing lacking from the rules are guidelines for making vehicle profiles and for designing arenas, but most people should be able to come up with something fairly quickly. Usually we just make some kind of oval with ramps and barriers. Then we scatter the vehicles around the arena. The freaks usually start on foot in various locations and then run to the vehicles to get them started. Wackiness ensues.