Argh! My biggest grammar pet peeve happens all the time. It's when apostrophes are misused. I just read a student's work that stated: "Advice for new grad's". New grad's what? New grad's inability to use apostrophes correctly?

The sky is blue. Thus, it's blue. If its blue, then it owns blue. How can a sky own blue? It can't.

The dog has a red ball. Its ball is red. It's ball is NOT red. That would be saying, It is ball is not red. Doesn't make sense.

More advice here. I want to meet that student's high school English teacher and ask her: WHY did you not teach this simple lesson? Let's (also known as 'let us') not perpetuate bad stereotypes in Alabama.