I hear ya... can't tell you how many times I've accepted an offer for butter only to be served margarine. (on the side, which I then avoid). It's especially offensive in an restaurant, where it says on the menu "butter" but they don't actually have any butter in the whole establishment. I consider that an outright lie and misrepresentation.
I just want to yell to the whole world
MARGARINE ---- IS ---- NOT ---- BUTTER!!!!!!
So don't call it butter!