Thanks for the responses ladies. I'm going to try to push parents to let it go for a few weeks. Maybe we can hype it up enough to get him excited for it in the meantime.

And to clarify, he's never cried/screamed over the potty at my house. He may not be exceptionally thrilled with it, but always goes the first time i ask regardless. I've told the parents I won't force him to go if he doesn't want to, especially at this point. Mom and dad aren't super knowledgable in this area and they've had more than one slip up like this (he said something once about "bad boys poop in their pants"), but they've been open to advice from me, which is one plus.