Someone so bad at a given task that the result is the same as if they hadn't completed the task at all.
Derivation: "auto out", an abbreviation of "automatic out" comes from a common recreational softball/baseball rule. If a team is short a player they must take an automatic out when that player would have come up to bat. Referring to a player as an auto out implies they contribute so little that the team might as well be playing short-handed.
The boss's son is such an auto out; I have to rewrite every report he turns in.