What then is an anti-masterwork? It should not be merely bad - incompetence is widely available and demonstrates nothing. Not should it be "outsider art", that is, made by someone who has no idea what they're doing or what the conventional techniques are. Rather, it should be aggressively offensive to the normal standards. Both layman and expert alike should recoil in horror from the determined ugliness. Trolling in craft form.
(fragmentary post, can be expanded on demand)