The line seen on a person's jaw or neck when their face makeup is too dark (or light) for their real skin tone.

I couldn’t care less (but one must keep up appearances, right?)

the well known wait at the tux rental place(normally found in a mall) the night before prom. "The line" is famously long because it normally includes many different schools from the area the mall is located in. It is normally characterized by comical impatience(often displayed by worthless kicking of the wall or air), male bonding, arguments, and even hackey sack playing.

When a man jizzes into the nostril of another person and covers their mouth so the person is forced to snort in the semen, as if snorting cocaine.

Prospective members of the gang are expected to walk between two lines of group members, while they are punched and kicked repeatedly. The prospective members are expected to walk to the end of the line on their feet. If they fall, they must start over, usually on another day, when the injuries have healed.

Refering to a womans clevage.
Is used to discretely point out major clevage

something nobody crosses