That’ll teach me to sneak a bite of someone’s peanut butter out of the company’s fridge. I’m working overtime and am starving, and found a jar of peanut butter in the work fridge. It smelled OK, but the taste was just a little off. Not spoiled, but unusually oily, I guess you could say. So then I took a look at the lid and saw the expiration date was May 2003.
So, is there anything interesting that’s going to happen to me and my digestive system in the next 24 hours?
The main concern would be oxidation - rancidity, which you’ve already noticed. There’s a slight chance of mold spoilage, but peanut butter manufacturers have to be pretty paranoid about keeping their product mold-free, because the peanuts can grow some pretty dangerous molds.