In a mixing bowl, combine olive oil, paprika, garlic powder, onion powder, brown sugar, chili powder, salt, and black pepper. Whisk until well combined.
Add the chicken thighs to the bowl and coat them evenly with the spice mixture. Cover and let marinate for at least 15 minutes, or up to 2 hours in the refrigerator for more flavor.
Preheat your grill or grill pan over medium-high heat.
Prepare the tangy honey glaze by mixing honey, apple cider vinegar, soy sauce, and red pepper flakes (if using) in a small saucepan. Heat over medium heat until warmed through, then remove from heat.
Place the marinated chicken thighs skin-side down on the grill. Cook for about 7-8 minutes until you see grill marks and the skin is crispy.
Flip the thighs and lower the heat to medium. Continue cooking for another 10-12 minutes, basting with the honey glaze towards the last few minutes of cooking. Cook until the internal temperature reaches 165°F (75°C).
Remove the chicken from the grill and let it rest for 5 minutes before serving. Serve with additional honey glaze on the side.