Once in class we had to do some kind of aerobic excercises, and you had to lift up your leg, so I did and ... farted
Kinda hard too
I also once was showing off to a friend, with a basketball, I bounced it between my legs and my shorts ripped. Luckily we were close neighbours
Oh yea, a recent one: I often scratch myself with my pen, so I was scratching along my leg, and didn't notice the pen was still on... So after class I asked if I could go home for another pair of jeans