Simply put, it's when one comes up with a thought, action, or saying that makes the user look like an idiot. From inventing odd techniques, like the drill or the jackhammer, to coming up with sayings that have no relevance in anyway to the current moment or conversation. Don't be sad though. Everyone has a moment or two. Some just have more than others.
Running into Family Mart while doing the drill in mid-air was a proud moment for everyone who saw.
You can stick that into your box of proud moments now.