Blend the coconut milk, lemongrass, cilantro, garlic, chili flakes, fish sauce, brown sugar, and lime juice until mostly smooth.
Place the chicken thighs in a shallow bowl and coat well with the marinade. Refrigerate for at least 1 hour.
Soak wooden skewers in water for 30 minutes before grilling.
Thread the marinated chicken onto skewers, alternating with pineapple, bell pepper, and onion pieces.
Preheat the grill to medium heat and lightly oil the grates.
Grill the skewers for about 4 minutes per side, turning occasionally until lightly charred and the chicken reaches 165°F internally.
Mix the peanut butter, rice vinegar, Thai red curry paste, and warm water until smooth for the dipping sauce.
Rest the skewers for 3 to 5 minutes before serving with lime wedges and peanut sauce.