tailgating

[2ndChildhood]

I always thought a compressed air tube shooting a yogurt container onto their windshield would do nicely. Never got stupid enough to try it though.

[Irving]

Remote controlled box full of sharpened jacks or roofing nails, located just under your rear bumper ought to suffice.

[TriggerHappy]

If you have an SUV, aim the rear glass washer fluid squirter to the rear, fill it with something other than fluid (sticky, stinky, permanent, etc.). Enjoy!