Call us what you will: Grammar Police, Grammar Nazis, Pedants, Jerks. Those of us who studied English in college (or, God forbid, grad school) cling to our knowledge like a buoy in shark-infested waters. We’ll correct your grammar in casual conversation, take a red pen to our books, and shout obscenities at billboards. Our degrees may not be worth much, but at least we don’t go around dangling our participles like gutter trash, thankyouverymuch.
If you really want to raise our blood pressure, make any of these mistakes:
1. Use an apostrophe to make a plural. I have no idea why people do this. “Apple’s” is not, in any language or universe, the plural of “Apple.”
2. Use quotations marks to emphasize a word. The “Blog” of “Unnecessary” Quotation Marks is a treasure trove of this bizarrely common error. “No” cellphones allowed…so cellphones are allowed then? Or are you just an idiot?
3. Write “could of,” “would of,” or “should of.” This one is less mysterious–but no less stupid. The phrase “could have,” when spoken aloud, sounds kind of like “could of.” Remember, you could have gone to Disney World if you had studied harder in English class.
4. Confuse “fewer” and “less.” Countless grammarians have torn their hair out over this at supermarket checkouts. “10 Items or Less” should really be “10 Items or Fewer,” since “fewer” applies to nouns that you can count. Beans, grocery items, pennies, pieces of candy–if you take some away, you have fewer than you did before. “Less” is used for mass nouns, i.e. nouns that describe something not easily broken down into individual units. You have less water during a drought.
Bonus Level: You have less time (mass noun) but fewer days/hours/minutes/etc (count noun).
5. Say “I could care less.” I get it; you don’t care. You’re apathetic. However, when you say “I could care less,” you’re saying that you have not yet reached the nadir of your ability to care. You’re saying the opposite of what you think you’re saying, and it makes me sad. What you really mean is “I couldn’t care less.”
6. Capitalize random nouns in a sentence. I saw this a lot when I taught remedial English. All nouns, regardless of whether they were proper or common, got a capital letter just in case. Look, unless you’re writing in German (those crazy kids capitalize all their nouns), there’s no Reason to make all of your Nouns feel special by giving them a capital Letter.
7. Write “everyday” when you really mean “every day.” This one gives me the fantods. “Everyday” is an adjective that describes something typical or ordinary. “Fresh fish everday” means nothing. I assume you’re trying to tell me, o ye hypothetical fishmonger, that you offer fresh fish each day of the week. Slip a space between “every” and “day,” and you’ll be fine.
8. Write “alot.” Allie Brosh, whose disappearance from the internet has left a hole that no one can fill, did this way better than I ever could: 
9. Make no distinction between “good” and “well.” This one is pretty easy to remember–”good” is an adjective, and “well” is an adverb. What’s that? You don’t…you don’t know what an adverb is. That’s just peachy. Just try to remember that English majors look good and do well with the chicks.
10. Don’t differentiate between homophones. There are two many of these mistakes to list. It peeks my interest, though; why do so many people not realize the affect they’re spelling has on the way others perceive them? Some days I just want use my red pin on the hole world.
Amen to that!