What qualities make Walter Mitty a humorous antihero?

Walter Mitty is a humorous antihero because he's not actually doing anything heroic at all. Mitty only dreams that he's heroic. His real life is uneventful, and he is constantly being nagged by his wife. In his dreams, however, he can be the person whom everyone admires instead of the person who is always getting picked on.
Mitty dreams of being a navy pilot while his wife admonishes him that he's driving too quickly (Thurber, 1). His wife nags him to put on his gloves, so he dreams that he's a famous surgeon who is prepping for surgery (Thurber, 2). A newsboy shouts a headline about a current court case, so Mitty dreams that he is an expert attorney (Thurber, 3). After running some errands, Mitty returns to his wife. She nags him again, and when Mitty protests that he was thinking of something else, she decides that he must be ill (Thurber, 4). Mitty's real life is dismal and boring, but in his head he remains "Walter Mitty the Undefeated" (Thurber, 5) and keeps dreaming up fantastic scenarios in which he is the hero.