Is there anyone on Earth who could convince John to quit drinking?

He didn't listen to his children, his mother, and I'm sure a "myriad" of other friends and family. Is it as simple as John's denial and belief that he is always right runs so deep that there is no one who could get through to him.

If Obama or Jay Leno asked him would he even humor the idea? I'm trying to think if there's anyone else he would listen to. They would have course have to have credits and of course John would have to gain from it somehow or he would refuse.

I believe there is one person on Earth who might have the power to do it but it's not in the method you think. The answer is: The Shit Weigher. If Shuli all of a sudden came out on his show and talked about how great drinking is for John and defended him as not being an alcoholic and kept going on about it, there's a 1.8% chance John might quit drinking out of spite against the person he hates the most.

Now reverse psychology is probably too rudimentary of a tactic to have an effect on someone with such an advanced state of NPD as John but it's a better chance than anyone else has, and such a childish motivation as spite seems logical in John's case.