The phrase is everyday Brazilian Portuguese slang, built from cheirinho, the diminutive of cheiro for smell, and merda, a vulgar word for poop. As a shareable audio clip it circulates mainly as a reaction sound in Brazilian meme edits and messaging chats, where a short rude line works faster than typing an explanation. Its popularity comes from that instant clarity: one sniff, one insulting description, and the whole scene feels gross. It remains useful because bad smells, dirty places and disgusting food are universal visual jokes.