similar to a dirty sanchez except before placing the penis on the person's face, you put a line of cocaine on top of the shit stained penis and let the person snort the line thus causing a "frosty" sanchez.
A sandy frosty is a sexual act where a guy is having sex with a girl on the beach. He climaxes by jizzing on a girls face then, unbeknown by the girl, throws sand in her face thus having the sand stick to the jizz.
Guy 1: Hey did you finally do it with Sarah on the beach?
Guy 2: Yeah and I finished up by giving her a sandy frosty.
Guy 1: That's gonna take forever to get off!