12. I was being taught how to dive in one of my swimming classes, I accidentally jumped in the 5ft deep (I'm too tall for it.) pool and I ended up getting my head smacked onto the pool floor. My swimming teacher lol'd. xD Same question.
Well, we don't have Fs here...but I remember one of my year 7 italian assignments being marked as "Ungradeable" (UG) so 12. Don't get me wrong, i was good at the subject...I just got lazy.
The lowest grade you can get in my school is a B. (Equivalent of a D in my country/F other countries.) I was about 7, I guess. When you had your first embarrassing moment.