Fill a cocktail shaker with ice. Pour in the vodkas and pineapple juice.
Cover and shake for about 30 seconds or until the shaker feels cold.
Put a maraschino cherry in the bottom of each martini glass. Strain the vodka/pineapple mixture into the martini glasses.
Slowly pour a little grenadine down the side of the martini glass so it settles on the bottom of the glass. Garnish with another cherry and pineapple chunks.
Notes
I used Pinnacle flavored vodkas, but you can use any brand you prefer.
This recipe makes three 5-ounce martinis or two 8-ounce maritnis. Yield will depend on the size of your glasses.