Sounds trite, but this can really work.

Ages ago I was in my boyfriends bedsit. I was drawing in a chair, he had fallen asleep on the bed. Suddenly I was overcome by the most tremendous rage against myself. Normally I'd have banged my head or gone looking for something sharp , but it was too overwhelming to do anything but attack my face with the crayon. that was in my hand. It soon rid me of what I was feeling - crayons being so waxy I became more preoccupies with making a crayon mark than hurting myself.

XXX