Doing it wrong. You slow down until you stop, that either forces them to run you over (way too obvious usually and might damage their car) or they get out and have a go, in which case it's really obvious assault but usually they are quite surprised that their tough guy powers disappear when they're not encased in a tonne of steel and they're now staring at a ragey bike rider who'd like nothing more than to embed a cleat in their face.
Did it to a bus driver tonight in fact, after he twice either punishment passed me or had no idea I was there. He fucking knew I was there after I was done though, the cunt. No, I won't stay behind your bus you fucking shit breather.