It doesn't get me outta their way. But once I can tell they're being a moron and passing, a tap on the brakes or stopping to coast a bit means the dangerous pass is done faster. This reduces the chance that the driver is in a head on collision... and a head on collision is extremely damaging. The large velocity differences mean that I don't want to be anywhere NEAR there.

And yes, they're large. A head on collision on a 25mph road ends up being a 50mph velocity difference. At 35mph, we're talking 70mph. That assumes no one is speeding... around here, it's common to see 35mph on quiet residential streets, and 55mph on streets posted at 30 or 35. The math gets very ugly, very quickly.