This.
http://www.optimummotorsports.com/smartycam.html
Not only do you get video, but you see EXACTLY what was happening at the time of the "incident". Imagine being able to produce details with respect to GPS positioning, speed, throttle position, brake status, etc. It'll even directly integrate to the ECU for even more data.
A friend of mine does race acquisition systems and uses these all the time. They're obviously a tremendous tool in a race application, but I always thought they'd be cool to use on the street for this very reason. They have direct support for BMW ECUs in the E9x generation, so I imagine F30 will soon follow. They also can operate standalone since they have built-in GPS and a 3 axis accelerometer.
Maybe I'll pick one up for the new F30 when it finally gets here. I've personally had 4 instances where someone tried playing a game. I'm the wrong sonofabitch to mess with so I won every case. But it's still a pain in the ass. Crystal clear video would cut through the crap in an instant.