Apology Not Accepted?

We had a little end-of-the-year lunch at work the other day, and the principal formally said goodbye to each teacher who is leaving with a little speech about each. There was one teacher in particular, who it was acknowledged, comes across as somewhat mean and short to other adults, despite being a very affective teacher that her students love. The principal said not to believe her tough exterior, and that she is all soft inside, and they both alluded to the fact that she had been through some stuff time in the past and that was why she acted so gruff all the time. During her little speech, she acknowledged all this and sincerely apologized if she had ever come across in a mean way to anyone, and that she sincerely doesn't mean to even though she knows she sometimes does. Although I don't work with this teacher as closely as I do with others, I can confirm, she does come across as grumpy 95% of the time. There are at least two other teachers at the school I can think of that have this same persona, and I'm sure every workplace has a few of them.

So, I guess that's nice that this teacher apologized, but maybe if you're aware of it you should make more of an effort to not come across that way? I'm not the warmest friendliest person all the time, but certainly no coworkers and few children would describe me as a mean or cold person straight away. If that's how people are known to perceive you, and you don't want them to, maybe you need to do something different. We all have our tough stuff to deal with; it’s not an excuse to just lack basic courtesy all the time.