It's basically a casualinsult If someone insults you and you want to get them back, but don't want to hurt their feelings too badly, just "flubberbucket" them ;)
A blob of slimy goo that defies gravity. Ranged in color from black to lime-green. Makes cars fly and basketball players jump to stupefying heights. From FLying rUBBER.
That's exactly what it is. Flyingrubber. IT'S FLUBBER!!