The mayonnaise was left out on accident?!

I don't ever refrigerate mayonnaise. I live on a boat with a tiny fridge in Mexico for the winter months.
Here's the thing....The mayonnaise won't go bad on it's own if left in the cupboard BUT any food that got INTO the mayo WILL.
If you NEVER put a dirty knife (or utensil) into the jar, the mayo is fine. If it's possible that food got into the mayo, turf it.
I always buy squeeze bottles of mayo to eliminate the possibility of contaminating it

Definitely. You Should Tell If It's Bad By Smelling It. Also, Overnight, The Mayo Grew From Cold, To Cool, To Lukewarm. This Means Bacteria Is Now Susceptible To Growing In It o_o Ewwh. So Trash It, For Your Sake. No One Wants To Get Sick :0

My personal opinion--I would smell it---if it smells ok--I would refrigerate it and next time it is used--smell again. As long as it smells ok and tastes ok---I would continue to use. Just me.

Smell it and taste a little, it should be fine.

>Naaah! I think it will be ok.

Was it Sam and Ella's Mayo? If so it is now properly ripened.

i agree with Charlies Davies. its mostly egg and oil.