I know you are all thinking, "Are you kidding?"
I wish that I were...but...
...no, I'm not. I see this one too often to remain silent.
Often the people using it incorrectly are native speakers.
Why? I guess this happens in school.
People think I'm talking about Americans when I talk about "phenomena" like this. To some extent, yes. But Americans do not have a monopoly on grammatical errors. In fact, it's more likely the British do.
So, which one should you use?
If you are talking about ownership, you use "your".
ex.: That is your car.
INCORRECT ex.: Your funny! <<<INCORRECT
If you are talking about the current state of a person in the second person, you use "you are" or "you're"
ex.: You're (you are) a real teacher.
INCORRECT ex.: You're mother is beautiful. <<INCORRECT
This is like saying "they're car," and it's ridiculous.
Some grammatical errors can be forgiven, but not this.
Remember, when you write on the internet, thousand or millions of people may see it. It is your responsibility to set the proper example.