What pisses me off: bad grammar

I was raised with an articulate understanding of the english language, so it drives me wild when people misuse simple elements that should be part of everyone’s general knowledge…
Do you agree?  Were you taught to speak the Queen’s english and get a little bit twitchy when grammar is used inappropriately?
Lets take a look at the words your and you’re… and the words two, to and too… These words are very commonly misused, and each time I see them I cringe for the person who has misspelled, knowingly or unknowingly.

Starting with your and you’re (Source: WikiHow)

You’re is a contraction or a combination, of the words you and are. Other examples of contractions include doesn’t for does not, they’re for they are, and can’t for can not.

*”You’re a good friend” means “You are a good friend.”
*”I don’t know what you’re talking about” means “I don’t know what you are talking about.”

Write your as the possessive form of you, referring to something that a person has, something that belongs to the person in question or, the person you are talking to:

*”Is your stomach growling?”
*”Your book is on the table.”

Now for two, to and too…
People rarely mix “two” up with the other two; it obviously belongs with words that also begin with TW, like “twice” and “twenty” that involve the number 2. But the other two are confused all the time, to and too. Just remember that the only meanings of “too” are “also” (“I want some ice cream too.”) and “in excess” (“Your walkman is playing too loudly.”). Note that extra O. It should remind you that this word has to do with adding more on to something. “To” is the proper spelling for all the other uses.

Are there any other grammatical issues that piss you off?