Characters who are eccentric, nutty or mentally unhinged tend to demonstrate this in everything - including language. They often invent their own words or use the existing ones in strange ways, employ peculiar syntax and grammar. From time to time, they may also use a Perfectly Cromulent Word.
Compare with Buffy Speak.
- Hinata from Haikyuu!! has a habit of describing things with sound effects, especially when he's excited. Other players occasionally do the same, such as Kageyama, Nishinoya when explaining receives, or Nekoma's Inuoka (leading to an excited and perfectly incomprehensible conversation between him and Hinata that consists almost solely of sound effects).
- Mizuki from DAYS is also highly prone to explaining things using sound effects and, in fact, incapable of issuing or understanding normal explanations. He also includes words from foreign languages into his speech sometimes, usually thinking they mean something other than they actually mean.
- Hay Lin from W.I.T.C.H. tends to use the words "spacious" and "cosmic" as synonyms for "cool", and also sometimes invents her own words like "weirdific" and "rockalicious".
- Delirium in The Sandman tends to do this occasionally-which make sense, since she's basically the personification of being a Cloudcuckoolander.
- Ever After High has Riddish / Riddle-ish. The rhyming language of the usually mad residents of Wonderland.
- In the Fate series, the Mental Pollution trait is explicitly described this way. Servants with the trait cannot be understood (or influenced) by anybody who does not relate perfectly to their disturbed worldview.
- Truth in Television actually. One of the common symptoms of schizophrenia is the tendency to invent neologisms.