In a large bowl, whisk soy sauce, brown sugar, vinegar, garlic, olive oil, salt, and pepper until combined.
Add the chicken thighs to the bowl and toss to coat thoroughly with the marinade.
Cover the bowl with plastic wrap and place in the fridge to marinate for 30 minutes up to 8 hours.
Place the oven rack in the upper-middle position. Preheat the oven to 400°F (204°C).
Line a rimmed baking sheet with foil. Then add a wire rack.
Remove chicken thighs from the marinade and place on the rack with the skin side up, shaking off excess marinade. (Discard leftover marinade.)
Bake for 30-35 minutes or until the chicken reaches an internal temperature of 165°F.
Broil for 2-3 minutes to make the chicken extra crispy and add a nice caramelized brown color.
Garnish with optional parsley and serve.