In a small bowl, combine the chili powder, granulated garlic, onion powder, cayenne, salt, and pepper.
Trim any excess fat from the chicken thighs and pat dry. Drizzle the oil all over the chicken, then rub all over with the spice mixture.
Melt the butter in a small saucepan over medium-low heat. Once the butter has melted, whisk in the honey, Sriracha, and vinegar. Reserve half the sauce in a small bowl for serving.
Preheat the grill on high. Brush both sides of the chicken with some of the remaining sauce in the saucepan. Place the chicken on the grill, then reduce the heat to medium-high. Cover the grill and cook for 3 to 4 minutes, or until char marks form. Flip and brush the chicken with more of the remaining sauce. Cook, turning occasionally and brushing with more remaining sauce, until the internal temperature of the chicken reads 165°F on an instant-read thermometer, 7 to 8 minutes more.
Before serving, drizzle the cooked chicken with the reserved sauce or serve the reserved sauce on the side.