Yeah Baby! This is what I like to hear! Mayo forever!
Chopped tomato, chopped onion, chopped jalapeño, mayo,mustard and ketchup.
A hot dog is a sandwich. All sandwiches except PB&J get mayo. Therefore, all hot dogs need mayo. It’s a simple fact of life. 
I have never, ever heard of doing this and my first thought was “EEEEEEWWWW!”
However, after so many “affs” coming in, I may actually try this.
Some day.
It’s how you construct it, too.
The mayo and the pickle relish must be spread together on the bottom bun.
The chopped onions go on the top bun.
Then the mustard goes on the dog.
yummmmmmmmmm
In all my life I’ve never seen this done. I feel so sheltered right now. An experiment is in order!
I don’t understand what’s the big deal. Here in The Netherlands all hot dog vendors have ketchup, curry sauce (like barbecue sauce) and mayonaise on their stand (and onions and sauerkraut and diced pickles). You’re supposed to put mayo on it.
But then, what is the deal with all those furreners fearing mayonaise?
Ahem, of course, you do realize all those who include ketchup on their hotdog assembly are being heretics to the One True Cecil…
Mayo is good, but I usually just put ketchup on it. I know, I’m a hot dog heathen. Whatever.
Sorry for the hijack, but just wanted to say that I mix mayonnaise and barbecue sauce together in a jar to make a dipping sauce for just about anything, hot dogs included. It tastes just like the sauce included with chicken fingers at many restaurants and the new dipping sauces that Heinz or whoever is putting out now. But it was my idea first! 
I like my hot dogs to be bombs, I put Mayo, ketchup, mustard, chili, cheese and grilled onions. I only eat this combination once a year or else I might die of heartburn. Since I live on the border of Mexico the way they do it here is they actually wrap a slice of bacon on the hot dog and they put raw choped onions, jalapeño, and tomato.
I dont see whats the big deal. I put mayo on my hot dogs before until they stopped offering them. I love saurkraut but mostly the good ol standby Ketchup, mustard and a little pickle relish and some bits of onion.
Thy put mayo on Big Macs. The “secret sauce” is really mayo, pickle relish and ketchup mixed with some sugar.