A phrase that can be used to respond to many different styles of comments, mostly opinions. This word originally derived from early Euoropean fox hunters, who had at first been pompous and arrogant and thought the fox to be a stupid animal, only to be outwitted by the creature time and time again. So this saying is basically a disagreement stating "remember our mistake with the fox", or, "do not assume this is true".
Gary: Hey Greg, you're gay!
Greg: Like a fox.