Whats the difference between "urs" and "up yours"?

I know my English isn’t anywhere near perfect (but far from it), and I am not as proud a linguist as I should be, but my jugular vein expands to exponential parameters when I see people who don’t know the difference between “you’re”, “your”, and “they’re”, “there” and “their”. It is time to take responsibility. There is no reason to be in high school and don’t know the difference.

I took a placement exam here in CSI (my mediocre college) . If I had to revise the English part of the exam, it would have two questions: One would be to define the difference between “your and you’re” and the second question would be to define the difference between “there, they're, and their”.

I bet 60% of the school wouldn’t be here.