I'm going to call my former boyfriend a fucking asshole.
Why would you call him that?
Because he called me a fucking idiot.
It's understandable that you want to respond to your then-boyfriend's rude behavior towards you. You should tell your boyfriend about how  his words make you feel and let him know that you will not accept his rudeness towards you.
Don't you start talking shit, don't you dare.
You should stop the name calling and just ignore them. You aren't together any more there is no reason you have to talk to him if he's treating you that way.