The story
From chimp + out, comparing the stereotyped behavior of black people to chimpanzees. Popularized in 2025–2026 by online figures such as Chud the Builder, at which point it began to be used in a nonracial sense (as, e.g., by 6ix9ine). The noun is a deverbal of the verb.
Etymology from Wiktionary, CC BY-SA 4.0.