This gave me another laugh! That's because I have NEVER bought a jar of mayonnaise, and that's because when I was 4 or 5, I somehow (I don't remember who told me what, and Mom didn't have a clue) developed a phobia about mayo, and wouldn't eat anything with mayo on it or in it! Fortunately, Mom and other family members would keep small amounts of things aside, like potato salad, and I would put my own dressing on them, and this was before this was a common thing to do. This went on forever, but when I was away at school, I actually taught myself how to make it, and used something from the co-op, that I had never seen before, and was basically not available anywhere, back then - Rice Wine Vinegar. That, and lemon juice, as the acid, are something I use to this day, when I occasionally make mayonnaise, to use for something. I called her, and told her to take a guess at the most ridiculous thing she thought I would make (she thought it was going to be some disgusting ingredient), and she couldn't believe it was mayonnaise. I still won't buy mayo or Miracle Whip, or anything that might have them in it.
And something I just remembered, that Mom did, because of my mayo phobia - she got a recipe from my neighbor, that was an almost black chocolate cake, and I've always loved chocolate. It called for 3/4 c of mayo, which makes sense, with the oil, acid, and more egg, but she wrote in the handwritten recipe 3/4 c sour cream* - the asterisk, in case I looked at the recipe!