They wore all black and in attempts to fight back against the popular athletes and jocks in the school, the Trench Coat Mafia ridiculed the jocks right back, attempting to stand up against bullies in the school.
On April 20, 1999, two students who dressed like members in the TCM and were also bullied outcasts in the school, Eric Harris and Dylan Klebold (who had friends who were members of the TCM), planted two home made propane time bombs in the school's cafeteria, and went on a killing spree in the school, carrying one Hi-Point 995 carbine rifle, a sawed-off Savage Springfield pump-action shotgun, a sawed-off 12-gauge double barreled shotgun, and a TEC-DC9 semiautomatic pistol, along with numerous pipe bombs, grenades, smoke bombs, and knives. They killed twelve students and one teacher, and injured 24 other students, before committing simultaneous suicide.
After the shooting, often termed as the Columbine High School Massacre, the Trench Coat Mafia became an infamous icon against jocks and bullies, and catalyzed a movement of outcast students sending a message in schools across the USA (and spreading to Canada and the UK): "if you mess with us, we might just come to school one day, and kill everyone in it."
DEFINITION: A group of students in a school who are social outcasts (usually the target of bullying and called geeks, nerds, loners), who wear all black and often black trench coats, and express a disdain for jocks.
Jock: "Those weird kids wear trench coats everyday, so they must be part of a Trench Coat Mafia, hahaha let's trip them up when they walk by and throw fecal matter on them in public hahaha."
Weird kid: *pulls out a shotgun and puts it in the jock's face and says "bang"*