I'm probably reading waaaaaay too much into this given little information, but here's my take (with added info!).
Player A (Julian Chase) decides that in his character's culture he would become seriously insulted should Player B continues to call him by his last name that he reacts angrily through the threat of violence. This makes for interesting scene of tension in a movie or book, but tends to come off awkward or as doofus-like if it's just out of the blue with no clue to the player and character to expect such a reaction.
For example, if the players know (metagame) the fact that Julian's culture would be offended and roleplays a character who is ignorant of it, then that's an interesting or normal scene to rp out. I know if I was the offending character, then I would then roleplay out the appropriate reaction and move on.
However, if the players don't know that Julian's culture would be seriously offended and obviously roleplaying a character who was ignorant of it, then as a player of the offending character, my first reaction to player A would be, "Dude WTF?!? How would I know that your culture would be offended? I didn't take Mind Reading 101 y'know." To me, it falls under the same kind of boorish behavior as a PC who just attacks another PC because "I'm chaotic neutral, it's my alignment dude."
Of course, I'm also speaking from the standpoint that the campaign is about a group dynamic as well. Maybe if we're all rp'ing jerks, cutthroats, or scum then that kind of outburst would be more of the norm than the exception.
I know, I know...probably read too much into this.
