Even if he believes in it, I think making this kind of wager is extreme. There are multiple other ways to emphasize your confidence.
$1 Million does look extreme. He has revised his prediction of $500K by 2020 to $1 million by 2020. And he has done this based on Bitcoin's strong rally in 2017.
It is obvious that he does not intend to fulfill his promise to eat his dick, that is just a metaphor the same way some people say they will eat their hats if something does not go their way, we should take this as what it is an attempt to bring attention to bitcoin and to make the general public even more bullish, I'm sure that many people around the forum will be happy if bitcoin reached 50k by 2020.
Agree,obviously if he said it he said it in a joking tone,that's pretty obvious,of course nobody would do something like that,it would not make sense,anyway,it seemed very risky to say that but maybe he did it to get people's attention only.