The phrase comes from Brazilian Portuguese slang, where rapaiz is a casual, stretched form of rapaz, meaning man or mate, and the full line asks in disbelief what something is. Shared as a short reaction clip, it spread through Brazilian meme pages and short video edits as a way to mark confusion at something odd, gross or unexpected. Its appeal is in the delivery rather than a specific show or film, and creators keep using it because the tone is instantly readable, funny and easy to drop over fails, reveals and strange everyday moments.