You're

Too oftenly mistaken for "your."

Meaning "you are." Used to describe something about someone, not something someone owns.

Correct example: "You're stupid."
Incorrect example: "Your stupid."

Are

Often mistaken for "r."

Describing something about a noun.

Guy 1: You am awesome, man.
Guy 2: You mean "you ARE awesome," you silly, silly boy.
Girl 1: You two be gay.
Guy 2: You mean "you two ARE gay."
Girl 1: I rest my case.