This was spoken by my sister-in-law recently. It is a nice mash up of “for all the marbles” (all the winnings or rewards) and “go bananas” (to go mildly crazy). My guess is that she was also thinking of “lost (one’s) marbles”, also meaning to go crazy. So the thought process went something like this, perhaps: marbles → crazy → bananas. Then again, a “top banana” is also the winner so maybe that was in the mix as well? Whatever the deconstruction, it is an excellent malaphor and hats off to Mercy Mamalis for uttering it!