Ex made sexual "joke" about my mother!!

This is more a rant than anything else, because Im just fucking pissed. Infuriated, sadden and so much more!! I just had my ex say my mom is fuckable, he would do my mom. This is a guy I had a 5 year relationship with, like who says that? 
My mother hated his ass, still does cuz he's 6 years older than me. And my mother always felt he was taking advantage of me. He is aware my mom dislikes him. So being pissed I told him my mother would never want his dumb ass. To which he replyed with, "How do you know that?" Honestly that just did it, mind you this is the same man that was trying to tell me he was still in love with me a few hours earlier. He tried to say he was just joking, trying to get under my skin. Well he did and I dont find that shit funny at all! I find that shit disrespectful, and disgusting. I would never sleep with anyone related to someone I've dated. And I wouldnt joke about that shit either. Like wtf, am I overreacting?? Cuz I feel like reaching through my phone and ringing his fucking neck😡😤