you hurt yourself. http://www.msnbc.msn.com/id/31852963/ns/health-behavior/ I've noticed that I tend to swear when I hurt myself and I generally feel better after that. I'm not a person to swear...only when I'm angry or hurt.
I swear all the time, almost sailor-like, except when in the presence of my superiors at work, children, or those I know are offended by it.