For 6 months, a coworker drove me nuts with stupid stories about himself. He would sleep on the job. Steal office supplies. He even left the job site without permission. I didn't really care about any of that, but one day I came to work to see that he had circled pay days on the calendar for the rest of the year as well as crossing off the days that had already gone by. This pissed me off so much that I reported him for everything that he had done for the entire 6 months. All because he marked on the calendar. I like clean calendars.