I have kind of mixed opinions when it comes to Neal and Peter banter, mostly because I don't see Peter as the type to use terms such as idiot or moron as a form of teasing. I could be wrong.

Rodney and John... though in this case I think John should protest much more, because Rodney can sound pretty condescending sometimes.

And I think this is why I have issues with the idea of Rodney calling John an idiot. John puts up with a lot from Rodney but he doesn't put up with everything (such as Rodney wasting time talking during a life or death situation). To me, if Rodney ever tried to call John an idiot, even if it was just playful banter, John would smack him in the back of the head. But, again, that's just me. I could be wrong, I don't know.