I worked at a restaurant chain when I was a teen named Friendly's (still around, but seemingly nowhere as big as it once was), and their big thing was the wide array of ice cream-based desserts. Among other toppings (such as hot fudge, marshmallow, and other sauces) was a peanut butter sauce that arrived in a gallon tub. When one opened it, they would find the oil had separated and was floating on top of this thick, semi-hardened dry sludge that was the rest of the PB. We had to mix it back up manually, and it had to be done thoroughly in order for it to work when put through the hand pump dispenser used to pour it onto desserts.

Yeah, I was never all that into PB anymore after that job.