CF violence is IC violence. If I pincer someone, usually it's understood that I don't want to pincer that player, just the player's character. A modern-sounding insult like "fuck you" however will come across as being OOC (whether it was meant that way or not). It seems like it was directed at the player BEHIND the character.
If we were really running around on a battlefield, trying to kill each other with axes, an insult like fuck you wouldn't seem so out of the ordinary. But we're not, and in the CF world it's pretty harsh. If you don't see the difference between IC violence and OOC insults, I'm not sure what to tell you.