I saw this and wanted to post it because I am guilty of this sin more than any other. I pity myself, for steps taken and not, for circumstances beyond and within my control. I punish myself daily for things that have happened years ago. In some ways it has made me stronger, I am my own worst enemy and being constantly beaten by myself means others can have no power over me. I still avoid people though, I still feel sorry for myself when things go bad, I still react negatively to certain things which don't warrant it.
I posted this because I know I'm not alone, everyone punishes themselves, we are our own worst enemies.
Someone made a cool cartoon of it too: http://zenpencils.com/comic/89-stephen-fry-ultimate-self-help-book/