It’s a slogan used as a protest statement, particularly within anti-establishment and anti-police movements. The acronym has a long history, particularly within subcultures like punk, skinheads, and football hooligans. It’s also associated with anarchist and anti-authoritarian ideologies.
This is true pretty much everywhere, even America.
Then why do Americans constantly say “all cops are bastards?”
It also originated in England.
America is not nearly based enough for Americans to “constantly say” that, unfortunately.