Wetting or messing your pants in public
I've been fortunate enough to only wet my pants in school twice.
In the third grade I did it on purpose to get out of taking a test. I was trying to buy more study time, but when I had to take the test the next day, I still failed it! That's karma, I guess.
In the eighth grade I broke my ankle and went to school in a full leg cast. I was bumbling down the hallway in my cast and crutches, trying to get to the bathroom, but I didn't make it and I wet my pants in the hallway.