Resolves to my own subjective opinion of what "as crazy" is, but I have a pretty high threshold, and however crazy it is it also has to be pretty expensive and seem pretty silly. Also I won't bet on this market. You should see it as your job to present evidence of billionaires doing crazy things to me and make the case that they're as crazy or crazier than these two events.
Additional criteria:
Can't be Elon Musk or Balaji, they already shot their shot this year.
Has to be by a billionaire
Has to be something crazy
1,000
1.00@Shump The stupid line city is pretty stupid, but they seem to have backtracked.
Building new cities in general is a pretty vanilla billionaire obsession; but whether or not it qualifies, they have to actually do it for it to count here.