I didn’t think suggesting ketchup on a fried egg sandwich was so outrageous - lots of people have ketchup with their eggs up here. Isn’t this common in your country as well?
I have known a few who put ketchup on eggs here, but around here Tabasco sauce or salsa are typical (for those who add anything) 🙂
I don’t know. I only know eggs with hot sauce. But I would try ketchup before I’d try mayo.