In general when people say “I want to tell you something, but you have to promise not to get angry/offended/etc.”, my response is along the lines of:
“I can’t and won’t promise that. I do promise that I will make an effort to temper any knee-jerk reaction I might have, and to give thought to your words and to my response before I say anything. I try to do this in all of my interactions with people whom I respect, but in this case I promise to make a special effort.”
And if that’s not good enough… well, then it seems my interlocutor doesn’t care that much about telling me whatever it is they wish to tell me.
These ground rules seem reasonable.
In general when people say “I want to tell you something, but you have to promise not to get angry/offended/etc.”, my response is along the lines of:
“I can’t and won’t promise that. I do promise that I will make an effort to temper any knee-jerk reaction I might have, and to give thought to your words and to my response before I say anything. I try to do this in all of my interactions with people whom I respect, but in this case I promise to make a special effort.”
And if that’s not good enough… well, then it seems my interlocutor doesn’t care that much about telling me whatever it is they wish to tell me.