In a large bowl, combine chicken thighs with coconut milk, curry powder, white sugar, and red curry paste. Ensure the chicken is well coated in the marinade. Cover the bowl with plastic wrap and let it marinate in the refrigerator for at least 20 minutes, or up to overnight for deeper flavor absorption.

While the chicken marinates, soak bamboo skewers in water for 2 hours to prevent burning during grilling. After soaking, thread 4-5 pieces of marinated chicken onto each skewer, leaving a bit of space between pieces for even cooking. Set the prepared skewers aside until ready to grill.

Heat a large skillet or grill pan over medium-high heat and add a tablespoon of oil. Once the oil is shimmering, place the skewers in the pan and cook for 3 minutes on each side. Look for a golden-brown exterior and ensure the chicken is cooked through, reaching an internal temperature of 165°F (75°C).

In a medium saucepan, add the remaining coconut milk, red curry paste, peanut butter, sugar, dark soy sauce, salt, cider vinegar, and a splash of water. Heat the mixture over low heat, stirring continuously for about 5 minutes until it thickens slightly and is smooth and creamy. Adjust seasoning if necessary.

Arrange the beautifully grilled Thai Chicken Satay skewers on a large platter. Garnish with chopped peanuts and optional cilantro or lime wedges for freshness. Serve alongside the rich peanut sauce, allowing everyone to enjoy this delightful dish together.