Yeah, it's tough for you. Your mom doesn't have the first clue what it's like to deal with something like a stutter every day of your life. You've endured things that would break her. She's supposed to be on your side no matter what. Maybe she did it as an attempt at a little lighthearted roasting or maybe she did it just to be a bitch. I don't know the dynamics of your relationship but I do feel like she should have known how it would make you feel. If it were me, I think I'd say something along the lines of, "you know mom, if there ever comes a time that you find yourself a lonely old woman who hasn't talked to her daughter in years, I hope you remember this moment." In any case, I am sorry you had to go through such an experience. I hope your mother wises up and apologizes to you for what she did and never does it again.