ACAB is a common slogan, especially in anarchist spaces. Should we really be using it though? It is a reference to children born without their parents being married, and due to christian morality is seen as inherently negative. It is effectively a slur. Do we really think that trying to enforce the hierarchies we are trying to get away from on others is going to help us? How have we allowed this slogan to become so common?
As an anarchist I think we should be defending these people, not punishing them with the hope of some of that transferring to cops.
There are variations such as your British style “all coppers are bastards” and the style I’m more familiar with which stands for “all cops are bad.”
sadly that doesn’t seem to be what most people mean when they say it, lots of people defending it in comments