Please diagnose whether the symptoms are consistent with a psychiatric condition.

I have a younger sibling who sometimes gets angry based on their mood and insults or ignores others.

Even when I'm feeling good, I become a very kind and gentle person, treating me well and giving me everything I need.

However, after always using harsh words, about a day later, when it's obvious that I'm angry, they apologize first.

I have depression, panic disorder, and bipolar disorder, which cause emotional fluctuations that I can't control. That's why I am receiving psychiatric treatment, and my sister is asking for her understanding. My true feelings are not like that; my sister is a really precious person to me, and if she apologizes by saying that, I can't refuse. But the problem is that this keeps happening repeatedly, and after observing for a long time, I realize that it's not everyone who behaves like that, but only those who accept and forgive me.

Basically, they only do that to people they find easy to handle.

He never does that to someone who is struggling.

Is this kind of selective anger really a sign of a mental disorder?

Or is it really because they think I'm easy to mess with and treat me casually?