I grew up saying "Yes sir" to my father in certain situations (like if I was in trouble or he was explaining something super important). My mother was much more laid back and I never called her ma'am. I have friends who grew up saying ma'am and sir to their parents. It doesn't seem strange to me.
Of all the weird things that have happened in the Hart family the "Ma'am" thing seems innocuous.
Being from MN, no one I ever knew used “yes sir or ma’am” except for a couple of exceptions. When we wanted to joke about someone being too bossy, we would say, “yes sir “ to either a female or male.
My friend’s incredibly sick and controlling and abusive husband made the kids say, “Yes sir.” Being from MN, we found that horrifying.
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