Let's ignore the stutter for now, there is no conceivable scenario where it is ever okay for a parent to insult their child like that. That is absolutely disgusting behavior for any parent to do. I'm so sorry - I dont have a good answer for this. It could be that they didn't think it as that bad to say, so having a serious talk with them and telling them how awful it made you feel could make them understand. If they're dismissive at this point, I unfortunately dont think they have the empathy or emotional intelligence to ever get it. Wish you luck.