This is a nice quick prank to pull on your co-worker, to make the color drain from their face, and their heart skip a few beats, as you sit back and laugh.
Step 1: Preparation
you will need a screw, a pair of linesman pliers, and a little bit of soft sticky rubber or hot glue
Carefully cut off the head of a screw, making sure to leave enough thread and point to be easily seen. use a small dab of sticky stuff and stick it to the dull side of the screw tip.
Step 3: Anticipation
Watch for the ideal time to approach the target. Ideally this is anytime you can set the pointy end of screw in place without being noticed.
If using hot glue, timing will be more necessary in order to be effective.
Step 4: Impact
As your co-worker is installing any accessory that would require securing it to a vehicle, in this case, an overhead video system, sneak up and stick your creation to the approximate mount location on the outside of the vehicle.
Try not to giggle too hard as you need to be inconspicuous.
Step 5: Enjoy
Just wait until the job is finished, and make sure they notice before delivering the vehicle to the customer.
This never fails to deliver a good old fashioned knee slapping good time. Even if the vehicle has a sunroof, and the screws would have had to be 6 inches long to reach there, the first reaction will be horror, for the installer at least...