For my own end, I tend to play my characters appropriate to their role. My Xeno, for example, considers non-libertonians to be sub-human and has a nasty word to say about all of them. My Bretonian characters have all had people close to them killed by Kusari, and hates them as a result. My KNF character doesn't particularly hate the Brets, but he fights them because they're the Emperor's enemies. He's a touch more courteous than my Brets, but not by much.
Now, having said all that, I do my best to stay away from anything insulting in RL. If one of my characters is saying something, I can assure you that it's meant entirely in RP, and I'm looking forward to your responses. Never do I intend any disrespect at all.
Now, looking at the bigger picture, I can assure you that the Bretonian players actually rather respect our KNF counterparts. Any intense RPing is exactly that, RP. We just get into our roles a lot, but it's really in good fun. If you ever think it's getting to be a bit much, just shoot a PM our way, and let us know.