When someone is beyond stubborn, use the word obstinate instead: "You obstinate old mule! Get out of my way!"
While stubborn may have positive or negative connotations, obstinate is most definitely negative, because it implies a kind of hard-headed determination not to change your mind even when it might be best to rethink your position. "The obstinate Man does not hold Opinions, but they hold him," wrote Samuel Butler way back in the seventeenth century. The word still does the trick if you want a put-down for someone you think is being a pig-headed fool or a stick in the mud.