For Malakaus, the only reason he's a reasonably well liked minor noble (From what I intended anyways) isn't because he treats people based off their class or standings, but quiet simply follows this ideal: Don't be a dick to people. Servants, slaves, prisoners, nobility, royalty, giving them a bit of respect and not insulting their dignity is hard, but doable. Trying to act above them just gives them an incentive to kick you in the shins. Now, that's not to say they are his equals (A double edge sword to be sure), but just because they might be their lessers doesn't mean he shouldn't treat them like someone he doesn't like.
Beyond that how he treats you mostly depends on if he likes you or not. If you're a good person, he'll muster the proper names and titles he should refer to you as, like how he typically calls Maria Knight Commander. If he doesn't, he might just call you by your name or what he knows you by. If he really doesn't like you, he might call you by your last name, full name, or whatever derogatory name happens to be most associated with you. Usually you're dead by that point though.