I work with one of these morons who just won't let it go.
So last year, I took the tax disc out my old Peugeot and bodged onto my Retro Raleigh with an HGV licence disc holder.
It took ages for the right moment to arrive, but one day I wheeled into work just as he was getting out of his car.
"Here he is again, using the roads for free" he said.
At which point I proudly pointed to the tax disc holder and politley told him to F### off.
He's never mentioned it since!