Run lime wedge (or brush lime juice) around rims of martini glasses. Place glasses upside-down on a plate with sugar to coat rims.
Add parsley, lemon juice, and lime juice to a cocktail shaker. Muddle.
Add some ice and pour in vodka and jalapeño simple syrup. Shake well.
Pour martini into two prepared martini glasses. Garnish with sliced jalapeños.