Hmm...
Have a friend in a firetruck spray someone into submission, then, as they struggle to get back up, bury them in cement from a cement mixer.
See how many people can fit in the bucket of a front-end loader (and see how fast it needs to move to remove them all).
Put a heavily armed friend in a cherry picker and let them go on a rampage from above.
Attach a heavy vehicle to a helicopter's winch and see how many kills you can rack up with your improvised wrecking ball.
The possibilities are endless...