Oh my MIL had a variation on this.
If we were having the sort of meal where everything was laid out on the table for people to help themselves too, not a buffet necessarily but, say, tapas, or afternoon tea or just a selection of savouries and salads, she would have to be offered every damn thing individually.
So when we sat down I would say to everyone "We have W, X, Y and Z and there is bread and salads, please help yourself."
Everyone would serve themselves except MIL who would sit there with an empty plate. So I would be going "Would you like some W, MIL" "Oh yes please"
"And some X?" " Yes please" and so on.
Finally I would serve myself and say again to everyone to please help themselves if they want more. But at some point in the meal I would realise MIL was sitting there again with an empty plate and I would have to go through the whole serving thing again.
I always thought she was trying to give the impression she was so gently brought up that she couldn't possibly help herself to things.