Is it okay/normal to say mean things to someone's face because they rejected you?

This may seem like bait, but I'm asking a genuine question. This happened to my girlfriend where she rejected her former best friend (in a nice way…

It’s never okay. This is the pathetic form of a defense mechanism that people with fragile egos use because their confidence is so weak that being told no is too much.

That person is not a friend and had clearly stated out loud how abusive they would be.