I think, under "fairness", there is another element - trying as hard as you can to react to the spirit of what other people are trying to do. This means forgiving OOC errors, obviously(1), but also reading and reacting in the best spirit you can.
For example, if it's clear that someone is trying to portray their character as friendly, but coming across as over familiar, you have some options: 1) React with hostility, 2) react cautiously, and be a little uneasy, 3) react as if they had just been friendly.
There isn't a "right" answer, but I think that you should give as much as you reasonably can. The key word being "reasonably". And it's obviously affected by your character and their viewpoints and everything else - situation, prior interaction etc etc. But it's about being cooperative, and that means buying in, at least a little, to the story that the other person is trying to tell, as well as your own.
(1) Example: Inept Minmatar: Of course, she is a Sebiestor.
Ept Minmatar: She's a Brutor. Idiot.
Inept Minmatar: ((Oh *swearword*. Sorry, my mistake.))
The fair thing to do is strike the whole exchange, and either do it over or just move on. The unfair thing to do is to refuse that, have your character assume that Inept Minmatar Character is a spy, spread that around to everyone you know and then do a little dance.