Prepare the Marinade:
In a mixing bowl, combine the pineapple juice, soy sauce, brown sugar, honey, vinegar of choice, sesame oil, minced garlic, grated ginger, and red pepper flakes. Whisk until fully blended.
Marinate the Chicken:
Transfer the chicken thighs into a shallow dish or a sealable plastic bag. Pour in half of the prepared marinade, setting the rest aside for later. Seal the bag or cover the dish, and let the chicken marinate in the refrigerator for at least 2 hours, or overnight for a more pronounced flavor.
Cook the Chicken:
Grill Option: Preheat your grill to medium-high heat. Place the marinated chicken on the grill and cook for approximately 5 to 7 minutes on each side, or until the internal temperature reaches 165°F.
Skillet Option: Heat a drizzle of oil in a wide skillet over medium heat. Add the chicken and cook for 6 to 8 minutes per side, until the meat is thoroughly cooked and nicely caramelized.
Prepare the Teriyaki Sauce:
Place the reserved marinade in a small saucepan and bring it to a gentle boil. Reduce the heat to a low simmer. For a thicker glaze, stir in the cornstarch-water mixture and cook, stirring frequently, until the sauce thickens and turns glossy.
To Serve:
Slice the cooked chicken and spoon the warm teriyaki sauce over the top. Finish with a garnish of chopped green onions and a sprinkling of sesame seeds. Optionally, add grilled or fresh pineapple pieces for extra tropical flavor. Serve alongside steamed rice or stir-fried vegetables.