it stands for "Sissy Boys Are Back In Town" and originated from "C M" when he heard some sort of commercial or something. To him and his friends it is used to refer to a couple of losers that they know but it may be used freely to describe anything that lame people think are cool.
The condition resulting from a men's bathing suit mesh getting filled with sand while frolicking at the beach, usually collecting in the area surrounding the perineum (sbab, taint, grundel, gooch), and bringing forth a gritty discomfort.