Acronym for Let's Just Shut This Fucker Down. To be said upon discovering alcohol fueled madness at a late hour in one's dwelling. Must be said after holding one's head in one's hands and running hand through hair with an exasperated look. Often paired with GTFO or the ego-syntonic PTFO (peace the fuck out).
Tom: "How many people in the hot tub?"
Drunk kid: "uh...10...no, 9"
T: "uh, LJSTFD. GTFO!"
D: "Oh fuck man, we gotta PTFO!"