Acronym for shut the fuck up. Commonly used by bad-ass kids on sites that filter inappropriate language, such as Club Penguin, Pandanda, Runescape and Stardoll.
Also incorporated by lazy typers who can't be bothered to find the hut he uck p on the keyboard.
Kid: "I like Highschool Musical :)"
Bad-ass kid: "Dude, stfu. No-one gives."