An acronym for Let's All Go Naked and Fornicate (or F*ck); originated in the late 1960's and seen on bumperstickers; the general public assumed it referred to some Air Force Base.
L.A.G.N.A.F.(white letters on blue background bumper sticker)
"What are we going to do this weekend? I'll buy a case of beer, let's head for the beach and LAGNAF!"