Slang suffix derived from キチガイ (crazy person). Attaches to nouns to label someone as an obsessive fan or enthusiast, often with a negative or mocking tone. Used in compounds like ゲームキチ (game freak).
See also: きちがい
彼は本当にゲームキチで、一日中ゲームをしている。
He's a real game freak; he plays games all day long.
あの人は車キチだから、週末はいつも車をいじっている。
He's a total game freak.
That person is a car nut, so he's always tinkering with cars on weekends.
Abbreviation of キチガイ (crazy person), used as a slang suffix to indicate an obsessive enthusiast.