Full moron is more than partial moron.

A partial moron might believe whatever he's told but then have a "wait a minute, something's not right here" moment. A full moron doesn't have that moment and spreads the problem to others.

Another example would be a "leopards are my face" moment. A partial moron would be surprised that approaching a leopard caused them bodily harm but learn not to do it again. A full moron would sue the leopard but do it again with their child.

Another example: a partial moron gets directions, sees the distance, thinks a half tank of gas will get them there and back despite prior trips showing the opposite. But they have a Jerry can in the trunk. A full moron wouldn't have the Jerry can and buys a bigger vehicle with a larger engine because it comes with a bigger gas tank and then blames the liberals when they still run out of gas.

Partial = recoverable, full = hopeless

JustZ is only saying Joe Rogan is a moron. The term "full moron" isn't a commonly used phrase on its own, but the word "full" followed by an adjective or noun can be used to enhance the descriptive word, such the quote "never go full retard" from the comedy movie "Tropic Thunder". The context is that an actor played a person with a mental disability in a movie, but they tried too hard, and the performance was uncomfortable for some people.

I feel compelled to note that I don't condone using hateful or disparaging language when describing the differently abled.