On the bike, the temptation is to change down a few and pull a wheelie away, but I always seem to fall off when I'm showing off! (When nobody can see me, I'm a wheelie god, honest!)
In the car, with the kids, I just ignore the 'gater and drive how I want to. If they want to risk it, I wanted a nice shiny new rear bumper anyway.
Last time I had this happen in the Soarer (some BMW thing stuck to my @rse), the scrote inside was all "hand signals", shouting and general bravado, and it looked like it was his girlfriend in the pax seat.
As we were approaching a roundabout with a backed up queue, I slowed gently, opened the door (checking the mirror first) got out and approached to have a friendly chat. I've never seen someone reverse, U-turn and leg it back the way we came so quickly. I'm not a small bloke but it wasn't like I was intending to hit him or anything! Highly amusing, and I bet he got lots of sex that evening for being so brave.
*Disclaimer- yes I am aware I was committing an offence by getting out of a running car on a public road, no need for the OCUK nanny massive to reproach me thanks!