). One then had to brake hard at a red light, so I pulled up on his left & told him, through the open passenger window, how fast I'd been going when he overtook me. Frozen, hands on wheel, pretending I wasn't there.
My favourite variation of this is to go upto the window with a big grin and say "I'd guess you didn't see the speed camera van then?" Hopefully they are bricking it for a few days when the postman calls.
