If you say, "I could of told you that." I will be tempted to punch you in the face.
If you text me and say, "I'm great you?" I will answer and say you make no sense.
If you write and say, "Oh don't worry, your fine." I will take a very deep breath, and move on.
If you even think of writing, "Their so great!" I may egg your car. You gave me permission.
If I find out you said, "How about we eat dad?" I'll suggest you love your dad, don't eat him.
I don't care if you're writing a letter, a paper, or texting a friend. I don't care if you're a reader or a strict, "I-don't-read-movies-are-better" person.
Please, for the love of all good on this earth, use correct grammar and punctuation.