Chuunibyo is a Japanese slang term that is used when referring to young teens(middle schoolers in particular) who are highly influenced by games and Japanese anime. This strong influence causes them to act as if certain concepts from fictional mediums are also applicable to the real world.
"Man why is (name) always act like someone out of a fantasy world. He's acting like a total chuunibyo."
by bigafrocj July 5, 2021