I moved from Iowa to Texas when I was 13. It was then I learned that "only Yankees put ketchup on their hamburgers" (same goes for hot dogs). I still use ketchup. Mustard will ruin a good burger.
I've lived in Idaho, Washington, California, Hawaii, Tennessee, Iowa, and Arizona.
I remember some folks in certain states got downright offended regarding the improper use of condiments the further East and South you went.
Around here, we have fry sauce, and it is the ONLY thing to use for fries and tater tots...
Fry sauce - Wikipedia
https://
en.wikipedia.org/wiki/
Fry_sauce
Fry sauce (commonly known as salsa rosada, fancy
sauce, burger
sauce, or mayo-ketchup) is a condiment often served with French Fries or tostones (twice-fried plantain slices) in many places in the world. It is usually a combination of one part ketchup and two parts mayonnaise.
And up here in Idaho, it is so much more than mayo and ketchup. Mayo and ketchup blended together is bland and does not taste like
real fry sauce.
Idaho Fry Sauce Recipe - Allrecipes.com
allrecipes.com/recipe/217152/
idaho-fry-sauce
Whisk together 1 cup mayonnaise plus 2 tablespoons mayonnaise, sugar, salt, paprika, ground mustard, and onion powder until smooth. Stir in the ketchup, vinegar, and Worcestershire
sauce until well blended. Cover and refrigerate until chilled, about 30 minutes. Store covered in refrigerator.
Store bought is nearly never as good as what the fast food places serve, but Stephen's isn't too bad...