Obviously lots of varying opinions as to what is acceptable within the confines of the game, and what is not.
For myself, for the most part, I behave in-game as I would out of game. When interacting with other people, whether it's face to face or virtually, there is a certain measure of decorum which I believe is required. It's not just another ship there, it's not just another dwarf/elf/whatever; there's another thinking, feeling person that you're dealing with. Just because you're not face to face with them, and because virtually you are mostly insulated from any retaliation should you upset them, that is no excuse to treat them any differently than you would any other person you deal with normally.
Within the confines of the game rules for confrontation with other players, whether it be blowing up other ships, or variable types of PvP which exist in other MMO's, or FPS's where the only objective is to shoot other players, I treat it as I would a sport. I play by the rules. I play fair. I play hard. Even if I am a terror on the battlefield (whether the case is or not may vary depending on game), I am a gentleman on or off of it. No insults. No hard feelings. No picking on the new guy who doesn't know how to pass the ball and misses every shot. Advice is freely given, if ever I have any. "Winning" is always the goal (definitions of which are variable and debatable so as such I won't go into them here, eg. defeating an opposing ship versus escaping from them), so no giving up if the odds are against you (eg. combat logging), but a victory is only worthwhile if accomplished by overcoming a struggle (ie. no picking on newbies, unarmed traders, etc.).
Some other real-life quirks which have crept into my gameplay: not only will I not trade in slaves of any sort, I also refuse to trade in legal drugs as well (alcohol, tobacco). Call me health-conscious or whatever.
Do I expect the same of others? No. I may hope for it, but as in the real world, you have to deal with all sorts of people. And regardless of how they may behave, it provides no excuse for me behave in kind.