Honestly I think that’s a valid point. Don’t get me wrong, I’m absolutely not a parenting expert, but my limited experience is that kids don’t consistently repeat behavior unless it gets them something they want in one way or another. I don’t buy that the cousins usual MO is to let the kid wear themselves out. I realize I’m making an assumption here, but my guess is the parents only ignored the tantrum in this environment because they wanted to enjoy the dinner, not because it’s how they handle the tantrum normally. Even though I think OP was being a bit of an asshole, I do kind of get where they’re coming from because tbh it would bother me too if they just ignored a disruptive behavior issue because they didn’t want to deal with it at the moment. But again, I’m certainly no expert, and I’m inferring context we don’t know for sure.