You know what irks me? People who grew up in an English speaking environment with English as the primary language of their country still mess up "you're" and "your". I don't know what to say, but in almost every comment that I see on youtube, facebook, twitter, all sorts of social media websites, there's at least this one person who uses your in stead of you're, or uses you're instead of your. It really enrages me, considering how English is not my first language, and yet I can still differentiate between the two and understand when to use which one.