A mason jar filled with urine that is intended to be thrown at people as a weapon, especially spies. Oftentimes, snipers will be caught using this weapon. Especially popular in the second Team Fortress.
I used my jarate on that spy, and now his suit is ruined! Ha ha ha!
Jarate, the "Jar-based Karate", is an unlockable secondary weapon for the Sniper. It is a standard glass mason jar filled above half-way with the Sniper's urine, capped with a screw-on lid.
Person 1: Im a TF2 Sniper main and I think jarate is a good secondary.
Person 2: Im a spy main and um, ew.
Person 1: "I learned how to do karate!"
Person 2: "Alright but I know Jarate"
Person 1: "What's tha-"
Person 1 gets interrupted as Person 2 throws a jar of piss, demonstrating how jarate works
Jarateed or "Jarate" is a synonym for "Pissed off" or "Piss".
It was derived from Valve's game "Team Fortress 2" in which the character, Sniper, uses a mason jar full of urine. The in-game name for it is "Jarate" and upon throwing said jar the character will yell "Jaaarate!"
Jarateed is also a word replacement for "pissed" on the Steam User Forums. The word filter will replace "Pissed" with "Jarateed". Clever reference on Valve's part.