Add the vodka, triple sec, lime juice, and pineapple juice to the cocktail shaker.
Place the lid on the shaker and shake until the shaker feels frosty and cold. Then strain the martini into two martini glasses.
Next, pour half of the grenadine into each glass. Pour the grenadine slowly against the inside of the rim of the glass; this will create the distinct layers.
Garnish as desired with pineapple wedges and maraschino cherries, and serve.