Was letting my mind wander, it got silly, my suggestions,
Just say you know about the tax thing, and you are truly sorry and that you will donate £210 or more every year to a charity for pompous, smug and unimaginitive drivers to fund the development of a new put down for cyclists as the old one is worn out.
Alternatively you can say, guess what, ride a bike and you too can avoid paying "Road" tax.
Or say, yes I save £210 plus every year and in not driving a (Insert appropriate make/model here, example BMW X5) plus everyone doesnt assume I am a c*nt !
Pretend to be deaf or Foreign, they love that
Say that you have been stopped by the doctor from driving due to some dreadful medical condition (make one up, Screaming Dutch Cock Rot, Twartyfagitis etc) and they will probably back down.
Get your cock out, that usually shuts them up, especially if you are a woman.
Ask if they are either a member of her Majestys Constabulary or Her Majestys inspector of taxes, when they answer no say "well f*ck off then".
Go red and strain in the face like you are having a poo.
Collapse theatrically then stop moving.
When they point out the tax thing, agree wholeheartedley and then put your bike in their boot and climb in the passenger seat, thank them for saving you from commiting a tax fraud and ask to be taken to your destination, freak them out further by talking like a Sat Nav unit.
Bark or make Chimp noises at them.
Hop onto the pavement and say "Happy now you road Captain"
Start singing the Banana Boat Song
Root through your rucksack muttering "Gun, Gun, hmm now where did I put it"
Grab their tax disk, stick it to your bike and pedal off.
Tell them you are actually car driver working deep cover to gather information on cyclists who commit this vile fraud.
If there are other cars or passers by, lean to the window of the car are pretend you are being throttle or shaken by the person inside, fall to the floor.
Start talking to them normally but stroke your bike and say soothing things to it.
Say twenty five quid for a blow job or 40 for full sex very loudly if anyone is about.
Get your mobile out and ignore them, talk down it saying that some prick is harrassing you, yes the road tax thing again, third one today.
Point in the back of the car say "JESUS CHRIST, WHATS THAT" and pedal off like your life depended on it.
Lick their car
Hand them an internet device, with the url of this thread or if you dont have one scratch it into their paint with a protractor.