Prepare Marinade: Whisk together 1 cup pineapple juice, ½ cup soy sauce, ¼ cup brown sugar, 2 tablespoons honey, 2 tablespoons rice vinegar, 1 teaspoon sesame oil, 3 minced garlic cloves, and 1 tablespoon grated fresh ginger. Add crushed red pepper flakes if desired.

Marinate Chicken: Place 2 pounds of chicken thighs into a bag or dish. Pour half the marinade over chicken, coat well, seal, and refrigerate for at least 2 hours, preferably overnight.

Cook Chicken: Grill or skillet-cook chicken thighs until internal temperature reaches 165°F, about 5–7 minutes per side for the grill, or 6–8 minutes on each side in a skillet.

Make Sauce: Pour reserved marinade into a saucepan. Bring to a boil, then reduce heat. Mix 1 tablespoon cornstarch with 2 tablespoons water; stir into boiling marinade and simmer until thickened, about 3–5 minutes.

Serve: Drizzle thickened teriyaki sauce over cooked chicken, garnish with green onions and sesame seeds, and serve hot with steamed rice or grilled pineapple.