Furious Goldfish - (Noun) - Someone whose ego causes them to argue against whatever their opponent is saying, even if it goes hand in hand with what they just acknowledged as being true, because they're simply too proud and angry to accept defeat. A furious goldfish appears to have an extremely short memory, akin to that of goldfish (short enough to cause them to forget and argue against their whole point in an instant), hence the "goldfish" portion of the term.
Original anecdote quoted from xoJane's blog:
"BIGOT: "Homosexuality isn't NATURAL. God didn't design two male lions to hump each other. It flies in the face of nature and the beautiful natural order of things, reflected in the animal kingdom since time began."
SOME PERSON: "Well, you know, there are many documented cases of animals engaging in homosexual behavior."
BIGOT: "Oh, the gays are proud of being like ANIMALS now?! You also see dogs licking their butts, should we all do THAT, too?!"
It's like ... can you not even ... follow ... your own logic?!? Is your memory that short?! ARE YOU LIKE A FURIOUS GOLDFISH?!"