Optional: Rim your glass with coarse salt or sugar by rubbing a lime wedge around the edge and dipping it into the salt or sugar.
Fill a cocktail shaker with ice.
Add tequila, sour apple schnapps, triple sec, and fresh lime juice to the shaker.
Shake vigorously until well chilled.
Strain into a margarita or cocktail glass filled with ice.
Garnish with a green apple slice and serve immediately.