I've had two serious ones
One was in an art classroom, kid strolls over and punches me in the eye, hurt like forget. So i got up and tackled him into a cupboard, knocked his glasses of (they broke) and we had a fight, everyone else in the class was yelling and stuff, we where covered in paint and he ended up crying and ran off, i got taken to the headteacher who didnt expel me because it was self defense, which was nice of him, and yeah, he never bothered me again!
Second one, some kid poured water in my bag which had my brand new (at the time) Blackberry Bold 9780 in it, i went mental and hit him in the face so many times, after it he ran off saying he was going to call the police, hilarious