Personally, I'm not generally deterred by cursing. I swear like a sailor in my own life, and I guarantee I've cursed while playing online too. As far as I'm concerned, there's nothing wrong with using an expletive or two as a reaction or in a self-deprecating manner. When you start directing these swear words at other people in a negative way, then it's not okay. Anyone who has ever had someone say “F-you” to them directly knows what I'm talking about. It doesn't feel very nice. It's not world-ending, but it's also not necessary. Be nice to your fellow players; don't curse them out.