Chuunibyou

Literally "second-year-of-middle-school disease," i.e. the affliction of a 14-year-old. It names the self-conscious posturing typical of early adolescence: acting like you're a special being, like you alone know how the world really works, dressing all in black, and delivering lines nobody asked for — the classic being "my right arm is aching…" (as though a sealed demon lived in it). The term is generally credited to comedian Hikaru Ijuin, who coined it on his radio show. It has since become a staple of anime and light novels, where whole characters get built out of it. You'll also see it written 厨二病, swapping in a same-sounding kanji borrowed from online slang to make the word itself look ridiculous — that spelling is the more mocking of the two.