Knocking off a wing mirror actually makes it more dangerous for all other cyclists on the road though, seeing as the driver now has a massive blind spot
I've managed to slam the mirrors on two cars forward, probably wrecking them, because they're designed to fold backwards. One occasion I was riding in a marked, but narrow, (bar width, just) cycle lane, with traffic moving at about my speed alongside. One dumb woman suddenly touches the brakes as I'm alongside, unable to see a brake light, so I carry on and hit the near side mirror with a hell of a bang, slamming the mirror into the door pillar.
The shocked expression on the woman's face was a delight to see.
The second time was in almost exactly the same place, this time some dimwit wanted something from the garage shop on the opposite side of the road, and couldn't be arsed to drive into the carpark, instead parking half on the footpath, half on the cycle lane, forcing me to ride into the stream of traffic.
In attempting to minimise the amount I was intruding into the line of moving traffic, I just happened to hit the offside mirror, slamming it forward. I believe I heard a tinkle of glass.
Before anyone raises the obvious question about personal injury, hitting a hard object with my knuckles at some speed,
my chosen type of cycling gloves, generally speaking, are Oakley Factory Pilots. Which have well-padded, carbon-fibre knuckle protectors.
Good for punching out side windows too, if need be...