I don't swear, for a variety of reasons - the closest I ever come to authentic bouts of profanity would be "hellfire and damnation!", which you can could say pretty much anywhere and not get a dirty look (though if you shout it at the top of your lungs while gesticulating wildly, you will still look and sound crazy). I don't have a problem with other people I know cursing, or media with excessive profanity (I love The Big Lebowski), but I don't ever feel comfortable dropping an F-bomb even if I'm repeating something verbatim.
Oh, also I occasionally aim "son of a *****!" at malfunctioning inanimate objects (which doesn't really make any sense when you think about it), or call my own flesh and blood relations bastards in a good-natured way (and thus insult myself by extension, which also doesn't make sense).