That was an obnoxious thing for your boss to do. That is absolutely NOT the way to help someone improve their performance. He should have had a private conversation with you if it is was a concern. It's one thing for a coworker to pull a prank like that, different if it's a boss.

Have you thought about why you don't close as many tickets? What % of your tickets get reopened compared to people who close quite a few? Are other people grabbing all the low hanging fruit?