Originally Posted by KRosh

Every few months there is a thread on GFY talking about the proper use of Your and You're

YOUR is a possessive adjective, indicating ownership of something
That is your sock.
Where is your potato?

YOU'RE is a contraction (combination) of you and are
Do you know what you're doing?
You're stupid.
The two are not interchangeable.

Getting it wrong makes you look stupid. And ugly.