Why don't people know the difference between when to use "you're" and "your"?!?!?!
It's infuriating. I see the incorrect use of these terms more often than I see them used correctly. What's so hard about it? "You're" is the abbreviated version of "you are" and "your" is usually used when referencing something belonging to you. e.g. "This is your needless rant on the deterioration of the English language". This sends a chill down my spine more than fingernails on a chalkboard...well, maybe not but almost as much.
Phew. Finally got that one off my chest. It's been bugging me for years and I've had no one to complain to.