My brother in law came up with this idea and it gets more and more tempting with every ride.
When stupid, ignorant motorists drive so close to you on your bicycle that you have to correct for turbulence, or when they pull out on you or cut you up on roundabouts, or when (and this really has happened to me) they throw their empty fish and chip wrappers at you, a bag of ball bearings tactically positioned within easy reaching distance - for example on the handlebars - would enable the infuriated cyclist to make a lovely job of the body work of any passing vehicle.
I swear one day I will do this, so give me some room or it will cost you - bastards!