The Brief: ACAB is an anti-police acronym that means "All Cops Are Bastards."

DEEP DIVE
ACAB (pronounced either “acab” or “A-C-A-B), is a politically-charged phrase that is heavily used in music and has been used in the many protests that advocate for the disestablishment of the police force in the United States. Originally coined in 80’s punk music, German band, Slime released a hardcore anthem called, “ACAB” which became popular throughout Europe’s famous hard rock scene. Due to multiple fatal incidents involving police brutality, this colloquial term returned to the mainstream because of the recent events that have sparked controversy and national protests in the United States.
Police departments across the United States are under much public scrutiny because of how officers have killed and enacted violence against unarmed Black people. They are being met with peaceful protests fueled by the anger of political leaders, celebrity figures, and everyday Americans. There are many musical groups, individual artists, and rock bands that have taken advantage of the initialism, ACAB to showcase their outrages towards policing in the United States which receives billions of dollars of funding a year. ACAB has transformed into a Twitter hashtag for users to show their advocacy for #BlackLivesMatter or other organizations that desire justice for police brutality victims like George Floyd and Breonna Taylor.
See How Twitter Users Are Tweeting With ‘ACAB’
news flash ⚠️ ACAB doesn’t mean all cops are bad it means all cops are bastardized. meaning corrupt. and ppl saying “good cops” are bad as well stems from them still working for such a corrupt system.
— t🧃 (@tennileh1266) June 10, 2020
ACAB that includes all of you pic.twitter.com/FkWgcRaLoR
— 🕸🧛🏻♂️ 𝔄𝔴𝔣𝔲𝔩𝔩𝔶𝔖𝔦𝔫𝔦𝔰𝔱𝔢𝔯 🧛🏻♂️🕸 (@hexxzander) June 14, 2020
now i’m falling asleep and she’s calling acab
— rebecca (@notrbccrlnd) June 6, 2020
For the people that say ACAB, make sure you don’t call the police when something happens to you.
— Charrise Lane (@CharriseLane) June 15, 2020
they just shot a black man based off reports he was sleeping in a wendys drive thru. ACAB.
ABOLISH THE POLICE.— Demetrius (@DemetriusHarmon) June 13, 2020