When someone calls you "Sista" or "Brotha", what do you do?

It irks me to no end and I just want yell "I am not your damn sister". But I think thats rude. Anyways, there is this lady that lives next door to my grandma that calls every black women she sees sista and it annoys me. What should I do? I dont want to be rude but I cant take it anymore.