Growing up my mom always called Miracle Whip "mayonnaisse" and I thought it was just a brand name of Mayo. Later in college I bought some mayo thinking it was the same and couldn't stand it. Still can't, but I like MW.
I grew up with Miracle Whip, I like it and mayonnaise both just fine. But my wife won't allow MW in the house, it makes her gag. I think they both have their places/uses, I don't consider them interchangable.
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I child-proofed my house, but they still keep getting in!