Update: I confronted my fiancé for name calling my son.

I asked my son for confirmation how he felt about my fiancé calling him “nimrod” and he says he doesn’t like it, it bothers him, and he feels that my fiancé is being mean. I told him not to worry, I would talk to him about it.
Well, I wanted to wait until my son was in bed, but my son spoke up and said to my fiancé “Mommy needs to speak to you. You keep calling me nimrod and it’s not fair.” He seemed to not hear him, just scrolling on his phone. I asked “Did you hear him?” He said “Yeah something about nimrod, but I didn’t call him that.”
Me: “Yeah but you’ve been calling him that”
Fiancé: “But I didn’t call him that recently..”
Me: “Okay but in general, you’ve called him that and he’s told you he doesn’t like it and you keep calling him that. ”
Fiancé: “But he calls me that too so I think he’s just going along with the joke”
Me: “He doesn’t understand the joke, he just feels you’re being mean. He calls you it back because he’s being mean back. ”
Fiancé: “Okay it’s just a joke but if he doesn’t like it then I won’t say it”
Me: “It’s not a joke anymore. He feels you’re being mean. Please stop.”
Fiancé: “Okay I just won’t say it anymore”
Please bear in mind that the entire time we are having this conversation, he is on his phone scrolling through social media and seems very dismissive like he’s just trying to end the conversation..
I’m over this guy at this point. wtf?
Trying my absolute hardest to become independent and move on with my son and my life from now on.