In a nutshell: unless you live in a tropical jungle or plan to leave the mustard out for years, the fridge is optional. Most experts agree that a cool, dark pantry is totally fine for months on end.
Next time you reach for that jar, ask yourself: “Do I want to taste the full, spicy soul of this mustard?” If the answer is yes, leave it out. Let it live its best life at room temperature.
And hey, if your grandma insists on refrigerating it, just smile and nod. Then, when she’s not looking, sneak it back to the counter. Some truths are worth fighting for—even if it’s just a little yellow squirt of defiance.