Am I the only one that put mayo on spaghetti and hotdogs, its like I replace the ketchup with mayo. ?

That does not sound appetizing to me.

cool...and  pasta salad using spaghetti noodles often also has mayo....ditto hotdogs.

Wouldn't know if you're the only one,but what does it matter? Have it your way.

Mayo on hot dogs isn't exactly unknown in the USA, but they use it more in Japan.  Spaghetti sauce is not 

ketchup" but putting mayo on spaghetti is pretty gross.  Mayo is just emulsified cooking oil.   Why drown pasta in oil?

Who puts ketchup on spaghetti?   Or hot dogs...haven't done that since I was five...

On Spaghetti? No. On hotdogs? Not really. I prefer mayo on french fries.  Or tartare  sauce. 

Spaghetti: yeah that's weird. But hotdogs I get.

you are the only one I have ever heard doing this

You're the only person I've ever heard of putting mayo on a hot dog, but I'm guessing you're not the only one on this huge planet.

Lots of people put mayo on pasta but it's usually served cold and is known as pasta salad.   

Most western people do not put ketchup on pasta so saying you're "replacing" the ketchup with mayo is odd.   That being said, I don't know where you are on the globe. My brother lived in Japan for awhile and he said if you ordered spaghetti in a restaurant, it was spaghetti noodles and ketchup. 

In my city if you order a dog with cheese, it may come with cream cheese.   Pfft.

Yea probaly cause I never anyone doing that before