Jancuk, also written dancuk, dancok, or jancok, is a well-known swear word from East Javanese slang in Indonesia, widely understood across the country as a rough, versatile exclamation. Closely linked with sialan, meaning damned or unlucky, it moved from everyday speech into Indonesian meme pages, gaming chats, and short reaction videos. Its blunt sound and instantly annoyed delivery made it a natural soundboard clip, reused for fails, bad luck, and mock anger long after it first circulated online as a reaction staple.