Cut the chicken thighs into 1-inch pieces and place them in a large bowl.
In a separate bowl, whisk together the soy sauce, honey, vegetable oil, rice vinegar, minced garlic, ground ginger, black pepper, and red pepper flakes (if using).
Pour the marinade over the chicken and toss to coat evenly.
Cover the bowl with plastic wrap and refrigerate for at least 1 hour, or up to 8 hours for more flavor.
Preheat your grill to medium-high heat. If using wooden skewers, soak them in water for 30 minutes to prevent burning.
Thread the marinated chicken pieces onto the skewers, leaving a little space between each piece for even cooking.
Place the skewers on the grill and cook for 10-12 minutes, turning occasionally, until the chicken is cooked through and has nice grill marks. The internal temperature should reach 165°F.
Remove from the grill and let rest for a few minutes before serving.
Serve the skewers with your favorite dipping sauce or over a bed of rice or salad.