I'm going to insult a depressed person about their depression after their being unreasonably rude to me.
Do you think that's the right thing to do?
I'm not sure. It's good to be honest, though. You should always do that.
You're right, being honest is a good thing, but insulting this person because they have depression isn't a good thing. They didn't choose to suffer from a mental illness, and you insulting them won't help anything.
Yeah, but I don't care and am going to do it anyway.
I think you should consider how they'll feel if you make fun of them for having depression. They'll probably feel terrible. I think you should just stop interacting with this person altogether.