One of the more disturbing videos goes like this: A naked man is in his kitchen with a glass jar on the floor. He squats over it so the jar goes up his ass. When it finally disappears, it shatters inside his ass. He then calmly proceeds to pick the broken shards of glass out of his profusely bleeding ass instead of calling 911. He does this without making a sound the whole time until he gets up and walks away and probably realizes he will die of internal anal bleeding and screams.
While it should be named 1 guy 1 jar, most people refer to it by the cup referencing
Person 1 "Hey friend, let me show you this video called 1 guy 1 cup"
Person 2 "This better not involve eating shit"
Person 1 "No worries dog, lets watch it"
Person 2 "Ur fucked up dude"
Person 1 "lol"