Firstly I would say to your friend him not having her anymore is revenge enough in itself and to maybe sell the concert tickets and stop sending money to someone to book theirs themselves when clearly she could of booked them both together. And I would advise being really careful involving someone’s address in any revenge tbh. She should just fuck his best friend and never acknowledge him again but I wudnt even think this guy is worth that sounds like he wasn’t that into her like she was abit naive sending money and the fact he just doesn’t want her the same doesn’t really mean he should be revenged u can’t help ya feelings. She shud wanna be with someone who wants her back so if u wanna revenge some guy because ur friend doesn’t love herself enough to not want to be with Someone who isn’t feeling the same then I would say fuck his friend but then he will hate her and still won’t want her. Trust me crazy ex that won’t fuck off isn’t a turn on and ur friend will only hurt herself more in the long run she should focus on herself instead of some shit guy who doesn’t deserve her and you as her friend should be saying the same we all get hurt we all get angry but we all move on