In a shallow plate combine the salt and ruby red grapefruit zest. Using the Key lime wedge, rub it around the rim of a rocks glass. Immediately dip the moistened rim into the sugar/ zest mixture. Set aside.

In a stainless steel cocktail shaker filled with ice combine the vodka and ruby red grapefruit juice. Shake until the shaker becomes cold and frosty, about 2 - 3 minutes.

Fill the prepared rocks glass with ice and pour the vodka mixture into the glass. Garnish with a grapefruit wedge or lime wheel. Serve immediately.