I can't find anything on Netiquette that goes into things like cursing, doesn't seem there's anything highly intelligent on this out there.
My belief is just play it safe, and gauge your anger, try to prevent anger by taking enough showers, getting extra sleep, working out as much as you can regularly. Use curse words to be funny. If you're highly religious, you can say, "My God!" Well, "Oh my God!" You can say an idea is shit, but people these days are extracting this. If you really feel the shit, don't crack open the shell and say it's to someone in particular. I never really on spot felt the need to curse in the worse. Make sure you know how much you are joking. I haven't even done it like this on my blog, let alone you think you won't get kicked out on an online message board.