One of the things I, personally, have had trouble with this game is being able to tell when someone is in character and when they are not. Every character (and real people) have a "voice," not merely a pitch and an accent, but a distinct combination of mannerism and idiolect. How does your character's voice differ from your own? Why is your character's voice the way it is, as opposed to yours? For example, Darius St. George speaks more flamboyantly than I do, because he's an influential socialite and he tries to put people off their guards.
I tend to find it hard to purposefully develop a character voice. I find that the characters I play generally start out relatively close to me and diverge into themselves the longer I play them. So far Lume is generally more tactical/clever and brutally-honest/abrasive than I am. She doesn't have the social graces or book knowledge that I do. (She has just enough social sense to know when to shut up, usually.)
Lume tends to be a bit meaner to Ajax (and others) than (I hope) I'll ever be to Michael. She likes the guy, but he's very different than her and she enjoys teasing him about it.
I guess I'd say that Lume is the way she is because of her experiences as a teenager. She had a relatively sheltered, middle class upbringing, but when she left home she spent a lot of time with a rougher and cruder crowd. She realizes that she's unlikely to get invited to any high teas, but in general has no interest in polite society or being traditionally middle class. If someone can't deal with her occasional tendency to be a bit abrasive, too bad for them.
Okay, so when you're speaking with a hard edge to your words, that's Lume?
I don't think it's quite as clear cut as that. She's not always that abrasive. Unless I'm blatantly saying something extremely stupid, discussing something that is not in game (ex. my laptop), or addressing the players by their rl names, I'm probably speaking in character.