When people write their eighth-grade graduation speeches all about how they're "moving on into the real world to apply all that they've learned." Yes, I know that some of them will not go to or finish secondary school, but most of them do.
1. You still live with your parents.
2. You're just going to high school. You're not moving to Boston and becoming a chief executive of some macro-monopolistic corporation. You'll probably have to write the same speech again in four years.
When people confuse their homophones and homographs. Not only messing up when they use such words (homophones: e.g. carrot, caret, carat [also karat]; homographs: e.g. bow, sow, hail), but also confusing the terms "homophone," "homograph," and "homonym."
When someone pronounces a word so poorly that you're almost certain he/she spelled it wrong in his/her head.
The fact that so many of the replies to this topic (including mine) consist mainly or entirely of dependent clauses.
Eating at Long John Silver's and finishing my drink half an hour before we get our food.