Not very often, although if I am annoyed and alone, I'll swear over and over. If I'm with my parents or small children, not at all. If I'm with friends, I'll only swear if I'm making a joke.
Although, coming from a public high school, not very often is still more than average.
Also, Captcha, how the fucking hell should I know what fucking visa signature cardholders get on friday? I don't even have a fucking credit card you dumb asscunt!
Shit!