You know what I reckon?

Fuck em. If they think your doing 50km/h over the speed limit when your actually doing 50km/h, then they can shove it up their arse.

What are they going to do, report you? Someone who is so blatantly wrong in judging speed is probably not going to be able to give a good description of your car, or even describe what you were doing wrong in a police report.

Just flip the bird, or yell abuse back at them. This normally makes me feel better when someone abuses me for being a "hoon", when I'm clearly not doing anything wrong