Green’s Dictionary of Slang

a.c.a.b. phr.

[abbr.; a popular tattoo in the UK, esp. among Hell’s Angels and other ‘outlaw’ groups]

all coppers are bastards.

[UK]Slime [title] A.C.A.B. (All Cops are Bastards).
[UK]The 4 Skins ‘ACAB’ [lyrics] Hangin’ around with my mates one night / We got in a little fight / Geezer come with a knife in his fist / I got cut along with the rest, said – / ACAB ACAB ACAB / All cops are bastards.
[UK] (ref. to 1945) Partridge DSUE (8th edn) 11/2: since, at latest, 1945.
98 Mute [Internet] Plow: What is your favorite song on your album and briefly explain what the lyrics mean? Jason: A.C.A.B. Plow: What does that mean? Justin: All Coppers Are Bastards.