Initially it was only the overuse of exclamation points that irritated me. NOT EVERYTHING NEEDS TO BE EXCLAIMED!!!!!!! There has to be a way to generate enthusiasm for a sentence other than tacking on a relentless stream of punctuation. I cannot believe that English is so devoid of substantive words or phrases to express excitement that we must resort to !!!!!!
Then the list grew. I've noticed my own unfortunate habit of adding ellipses between thoughts in emails and other forms of communication. I don't find this nearly as annoying when I'm communicating casually; however, the habit itself makes it much more challenging to write a formal email without the lazy pausal dots interspersed between thoughts. So, I'm falling prey to...wait for it...writing like I speak. Where an "uh" or "um" would be uttered in verbal conversation I put "..." to indicate a pause or lost thought in written communication.
Yet another irksome trait that frequently appears in my students' writing: repeating words or variations of words in the same sentence, subsequent sentences or even within the same paragraph in a giant tribute to laziness. I admit my own vocabulary is not developed to the point that I can recite a thesaurus, and I completely understand when students for whom English is not their first language choose to use the same word repeatedly. But, "conflict is destructive and causes destruction" is just not a useful contribution to any line of thought.
I'm guilty of all of the above. And it annoys me when I do it too.