an imaginary fish from JD Salinger's short story called "A Perfect Day For Bananafish" which is found in the book 9 stories by Salinger. According to the main character of the story banana-fish are fish the swim into coral reef and holes in rocks to eat the bananas growing there but then eat too many and cannot swim back out and then die because of this.
Bananafishbones, or bananafishbonesing is a state in which you are unlike yourself and engaging in serious crackhead behaviour. Derived from the song by The Cure of the same name which is not only fairly chaotic but embodies the mood and general energy of it to a T, to go Bananafishbones is to simply lose all inhibition and tweak the fuck out.