My mum used to cut my hair with clippers when I was younger. One time, the black clipper bit that fits on at the end just flicked off as she turned them on. She didn't realise it flew off and did a straight line up the back of my hair on a grade 0.
My hair looked like one of those prank they did on Jackass, where they creep up behind people and shave a bit out of their hair
