If a MarySue is "perfect", then the easiest way to avoid making one is to do the opposite, right? Well, the AntiSue shows up when an aspiring writer takes the opposite of "perfect" as "perfectly opposite" instead of "imperfect". A MarySue is a FriendToAllLivingThings who is [[SoBeautifulItsACurse So Beautiful, It's A Curse]] and can solve any problem in five minutes or less? Then an AntiSue will be TheGrotesque and an EnemyToAllLivingThings who [[FailureHero never does anything right]]. And so on.
Unfortunately, simply [[InvertedTrope inverting]] the CommonMarySueTraits does not prevent a character from being a MarySue. When other characters still worship her and the plot still bends over backwards to facilitate her, she's still a MarySue, despite now being described as an unspeakably ugly and incredibly pathetic loser. This can actually be even more annoying than a vanilla MarySue — at least it makes some sort of sense for characters to worship a beautiful, friendly, hypercompetent MarySue, but when they're physically ugly with an unpleasant personality and can barely tie their own shoes (much less solve other people's problems) and everyone still treats them like the greatest thing since sliced bread, WillingSuspensionOfDisbelief gets smashed into tiny little pieces. (And yet, this is sometimes OscarBait for movies about the InspirationallyDisadvantaged)
Compare and contrast SuetifulAllAlong, a less extreme attempt to avert CommonMarySueTraits. Also contrast JerkSue. Not to be confused with "Auntie Sue".
'''No examples, please; this just explains the term.'''