Well! I GOT one that wasn't "once"! It was just now! I smoke and a tiny piece of cigarette ash fell on the keyboard as I was typing. I typed an 'I' and in the next work I typed an 'i' and then... I couldn't find the 'i' for the next word. It disappeared! That's when I realized I had two 'j's on my keyboard.

Well, *I* think it qualifies.