In Judeo-Christian and Muslim traditions, the day at the end of the world when God judges the moral worth of individual humans or the whole human race.
guy1"Come Judgment Day, I bet I goto Heaven"
1: The day your parents find your stash of marijuana.
2: The day your girlfriend finds you at a strip club
3: The day in several fucked up religions that state the end of everything.
4: The day SkyNet takes over
Mom: What the FUCK is that green shit u got under your bed?!?
Kid: Chewed up froot loops?
Bitch: Marty what the FUCK are you doing here at this strip club??
Marty: what the fuck are YOU doing here, bitch?!?
Christian Bigot: OMFG THAT GUY KILLED MY FAMILY, JUDGMENT DAY IS COMING!!!
Me: (shoots him dead)
Sarah Connor: 3 billion human lives ended on August 29th, 1997. The survivors of the nuclear fire called the war Judgment Day. They lived only to face a new nightmare: the war against the machines. The computer which controlled the machines, Skynet, sent two Terminators back through time. Their mission: to destroy the leader of the human resistance, John Connor, my son. The first Terminator was programmed to strike at me in the year 1984, before John was born. It failed. The second was set to strike at John himself when he was still a child. As before, the resistance was able to send a lone warrior, a protector for John. It was just a question of which one of them would reach him first.
The day you get back the results of your STD test.
Dude, it's Judgment Day. I really hope it's not herpes this time.
The day in which one's parents become aware of one's marijuana usage, usually followed by arguing or discussion where one will feel as though they are being judged.
Mike: "I faced Judgment Day last night."
Rick: "How did the folks take it?"
Mike: "Apparently they were old hippies, so it's cool!"