Here in Cameroon mayonaise is a popular condiment, and most people do not have access to refridgerators. It’s left on the counter, generally in 100+ degree heat. For the most part people are fine.
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Yeah, but it’s that “least part” that was worrying me. 
I worked in a commercial kitchen for years during high school and college and we never put mayo in the fridge. Of course, we used a hell of a lot of the stuff and it wasn’t around long, but the opened jars of it were out on the shelves for days at a time. No one sick or dying.
I did that when I was a kid. I didn’t like any kind of salad dressings that my parents kept in the house, so I would put MW on salads. It was ok then, but the thought kind of makes me gag now.
I like them both. I usually get mayo but I’ll buy a jar of MW once a year or so to change it up a little.
Every once in a while I get on a health food kick and buy light mayo (or, if I’m really delusional, fat-free mayo, god help me) but that’s usually pretty short lived.
I tried it once. Not horrible. You can make a respectable Thousand Island substitute by mixing mayo/MW with ketchup, relish optional.
And yes, I conflate the two. Neener.
Morgyn, look on the jar label, carefully, for the phrase “Refrigerate After Opening.”
It isn’t there.
On the back label, right next to the nutritional info and under the little “Kraft” symbol:
Refridgerate after opening
Do not freeze
Am I first? 
The one in my 'fridge says it on the lid, but it’s right next to the pickles which also said it on the lid and I’m pretty sure pickles don’t need to be kept cold. Probably a lawyer thing.