In Western Europe and much of Asia, almost nil (countries like South Korea, Japan ...) In many countries, I'm afraid it's quite common, abuse of police power is nothing strange here. I've had it happen to me.
South Africa (Pretoria). And by, I've had that happen to me, I mean Police intimidation, not a flashbang in my chest. For that sort of thing see Palestine, Iraq etc However we see abuse of Police power very often here.
You can see police intimidation everywhere. Even in Slovenia and other EU countries, I believe. But there is a difference between "go home, you're drunk" (even though you have a legal right to be there) and "BANG! BANG!".
What's the incidence of things like this in the rest of the world?