How should I try to make my friend understand that her new boyfriend is a toxic psycho?
Why do you think he's a toxic psycho?
He's made many nasty and rude comments to me and others, he's not very nice.
I'm sorry he did that to you! I think it's a sign of a good friend that you're trying to warn her about this new boyfriend of hers. You should tell her what he's said about you and others.
I hope she's willing to listen to me, she needs to know the truth.
Make sure you talk to her in a calm and rational way. If she really likes him, she may think you're jealous and trying to sabotage her relationship. Tell her how hurtful his comments to you have been and help her understand how serious this is.