Is it normal to mix ketchap and mayo/

It's called a fry sauce totally normal and tasty

Probably not many people do it, but if it tastes good to you go ahead.

Ketchup and mayo is the secret sauce.

Depends where you grew up. It's definitely a local custom. Nowhere in Canada that I've been, and I've been coast to coast, uses mayo except on toasted bacon and tomato sandwiches.
Some burger joints premix it and put on your burger but I just scrape it off and replace it with straight ketchup, not that there's anything wrong with gay ketchup.

Growing up, my dad would mix ketchup and mayo together all the time, and my siblings and I would put the mixture on plain hamburgers. It was actually really good.

Ketchup + Mayo = Golf Sauce (check Wikipedia)

yeah my friend likes doing thisnot weird at all

I mix mustard, mayonnaise and ketchup, then I add either Tabasco sauce or Louisiana Hot Sauce or both!

Normal. I used to do that and put it on my cheeseburgers. Sometimes I'd mix relish in it too.

I mix mustard and mayo. Sometime I add BBQ sauce to the mix. Yummy.