For some reason poor, discourteous drivers around me doesn't make me swear. I expect nothing more from them than overt stupidity and they consistently deliver.
I do swear when I stop thinking about what I'm saying and I'm excited, but I do wish I could better control my tongue.
But I totally understand the feeling of cutting loose with a string of four letter words now and again to blow off steam. Alone in a car is probably the best place to do it, but only if you leave your handgun at home