My recent ex LTR treated me like this, on 4-5 occasions over the course of three months. Two of the last times I broke up with her, called her out, and just lashed out because I couldn't take it. Said a bunch of mean things, which in hindsight I totally dont regret, because of the way she tried to embarrass me in front of family and friends. Spent the last three months ranging from "did I overreact??", to "of course I overreacted, no woman has ever treated me like that, and she was a narcissistic bitch."
She was a cold hearted narcissist. Since then I have learned what they are. They suck. You cant reason with them or expect any empathy. The narcissistic relationship pattern totally followed this. These women exist. They use you for entertainment and validation. The only way to deal with them is 1) totally avoid, and 2) if you are mad, call out their weaknesses. They will likely discuss their weaknesses with you, because they always do. A crooked chin, sagging ass, increasingly growing upper arm girth, etc. Or just make one up. Mine was abnormally upset about her age, she hated her birthday. When she was screaming at me "Your too precious", I simply calmly said twice, "you should learn how to treat a man soon" referring to her age. Thats all it took to send her into sobbing tears. Mission accomplished.
Rather than get ugly, just avoid completely. I was afraid I would look like your friend, all it took was a few times it happened over a few months for me to hit the wall and blow up the relationship. Your friend needs to learn these lessons on his own. Let him face his own weaknesses. If you really want to get back at her I would just take him out at night around other girls, strip club or even get him action. That will likely blow them up for good.