When you are getting your your junk pounded on by a significant other (e.g., a partner, stranger, lover, hornswoggler) whose hands are sandy af.

The act of really going to town on someone's private parts with hands / feet filled with sand.

A "Sandy Handy" but with a little more gusto!

This is a non-gender bias term, anyone can give or recieve a montauk mash job as long as thier extremities are sandy and you are really "just mashing it." You also don't have to be in Montauk, or on a beach.
"Whoa look at those two homeless guys giving each other Montauk Mash Jobs under the boardwalk" -- an angsty teen witnessing a grown man receive a sand filled hand job on Long Island

"Yeah she gave me the ole' Montauk Mash Job" -- a guy with severe sand burns on his dick

Guy 1: "She was trying to grind my dick into dust with her sandy hands"
Guy 2: "So she gave you the montauk mash job"
by #SquidKid March 14, 2017
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