I usually do it. Whether it does any good or not depends more on the driver than on me. If I judge that someone has endangered me through ignorance or stupidity, then I try to remain calm, polite and constructive. If I judge that the manoeuvre was borne of malice, I treat it more as therapy. A nice elderly fellow passed me at about 40mph six inches from my elbow last week, before turning into a school to pick up what I presume to be his grandchildren. The subsequent exchange went like this:
"You need to give me a WHOLE LOT more room than that."
"I'm sorry. Something was coming the other way and I had to squeeze over."
"You should have seen it coming. You just have to wait. It's really scary when you pass that close."
"I'm sorry"
"OK. Thanks. Just do it differently next time."
He did look a bit scared, mind.
A bit longer ago, two young women roared past me in an open-top vehicle and shouted something along the lines of "Get on the f**king prom!", laughed uproariously between themselves and then turned into a car park (drivers are not the cleverest people). It was the sort of car park one might park in for a stroll along the seafront and an ice-cream. I followed them round it, pulled up behind their car and engaged Calm Psycho mode.
"Were you talking to me?"
They looked round, visibly terrified.
"Er, um... we just wanted to know why you weren't on the bike path."
"Sure you did. That's why you asked me a polite question and waited around to listen to the answer."
Silence. Worried looks exchanged.
"You're lucky you picked on someone as affable as I am." Pause. "If I were to go round shouting abuse at strangers, I'd be worried to leave my car unattended afterwards." Pause. "Just in case they decided to rip the wing mirrors off." Pause. "Looks expensive."
For some reason they appeared to change their mind about the stroll and the ice-cream.
Readers may make up their own minds as to whether such exchanges do any good. Both of them made me feel better.