(1) tell your mother to go fuck herself;
(2) tell her in front of your daughters; and
(3) realize that it was the fourth or fifth time you'd said it to the old broad that day.
Luckily, when I told my oldest, in a later moment of partial calm and partial recovery, that I couldn't wait until I was in my eighties and she told me to go fuck myself, my daughter responded:
oh dad, don't worry -- you don't have to wait . . . .