It's rude to make people feel inadequate.
John and Mindy are at home and Mindy asks him how to use the dishwasher.
John wants to feel good about himself.
John gets up and shows her how to use it and says she'll be an expert in no time.
John tells Mindy only an idiot would ask that question, and she must be dumb.
Mindy feels loved and closer to John and confident with the dishwasher.
Mindy resents John and wonders if he really loves her.