Yes, I know the title isn't grammatically correct, but I think it is an acceptable exception.
How you write, and speak, says a lot about you. It doesn't matter whether you are in a formal or informal situation, if you do not communicate well, you will be judged less intelligent. The key is to use language that is appropriate to the situation. Some things that may be acceptable in an informal situation might not be in a more formal situation.
Regardless, it is stupid to use incorrect grammar, spelling, and sentence construction. Sometimes there is a fine line between incorrect and accepted deviations. As an example, "C U tomorrow" is perfectly acceptable in a text or email message, maybe even in an informal letter. But, "Your an idiot!" is just plain wrong. (In case you are stupid, "Your" is the plural form of you. "You're" is the contraction for "you are", which is what is meant in this situation).
When a particular error is used enough, it might become standard usage, and therefore correct. The English language has grown over the years, and rightly so. But no amount of usage will make plain old wrong right.
In future posts, I'll cover errors I see and how to do it right.