This starts having the guys do a stunt where they go down a zipline and get pelted by paintballs. Everything works fine the first couple times and the stunt goes on filming.
Then Steve O gets on the zip. While everyone's had parachutes that help slow them down at the end, Steve O instead gets rigged with a jetpack of sorts (you can use a leaf blower or put a motor directly onto the pulley system where the harness attaches to the line).
When he gets going everyone nails him with paintballs (and giant fly swatters like was suggested before). As the end comes near, when he's supposed to pull the parachute, the motor/jet pack activates, really rocketing him towards the end of the track.
As he's seemingly plummeting to an extremely hard landing, the end of the line has been modified so that he gets sent flying off the line into the trees. Hiding behind the trees is an air cushion, but nobody knows that beforehand.
Surely everyone will be surprised as Steve O is rocketed screaming like a girl into trees.