Is being a mean person a moral flaw? When you do it to hurt someone's feeling intentionally or course. But that doest necessarily mean the intended person is offended in any way. If they appreciate it instead for some reason and no injustice is felt, was said person being mean or simply trying to be? So you can seem mean without trying. You can seem passive whilst attempting to be mean and anywhere in between. What's more, if someone is being mean on purpose, and they succeed, assuming they are judging their own personality, would it not be considered as good? Justified in some way? Simply achieving a desired effect in anything is positive reinforcement.
Truth is meanness can be felt or dished out and it can be either just or injustice. meanness can be felt even when the intentions are good or vice versa. And when it comes to if its a personality flaw or not, again, relies mostly on the judge because what some see as simple retribution or maybe punishment for a wrong, looks to some as mean, others may find it immoral and some think it's all a joke.
Have you ever told a kid off about something and mid sentence realised you had the wrong end of the stick. Then you feel bad for being mean. Even though it felt completely justified a second ago? Therefore it wouldn't be fair for any judge to count meanness as something immoral, being as it pivots on understanding of a situation. My son is 7 now and he gets what mean is. Although many time he considers something mean because he can't see the good in it or he will not realise he's been mean because he couldn't see the bad in it. Meaning what's actually mean, doesn't mean anything.