ex-nerd; former otaku; someone who has given up geeky hobbies
Refers to a person who used to be deeply into anime, manga, games, or similar subcultures but has since left that lifestyle behind, often including changes in appearance and mannerisms.
See also: オタク
He gave up his otaku lifestyle and now works in a suit.
Aiming to become an ex-nerd, I sold all the figurines in my room.
Compound of 脱 (だつ, 'escape from' or 'de-') and オタク ('otaku'). The exact origin is uncertain, but it follows a common pattern of 脱～ words for leaving a state or identity.