Grind peppercorns coarsely using a mortar and pestle, electric grinder, or spice mill.

Chop cilantro finely and transfer to a mixing bowl. Stir in the freshly ground pepper, oyster sauce, soy sauce, fish sauce, oil, and cayenne. Add chicken thighs and toss by hand until completely coated. Cover with plastic wrap and marinate in the fridge for 4 to 12 hours.

Combine rice vinegar, lime juice, garlic, sambal, fish sauce, cilantro, and honey to make the dipping sauce. Refrigerate until ready to use.

Preheat grill for medium- to medium-high heat and lightly oil the grate.

Place chicken thighs on the grill, discarding any excess marinade. Cover and grill until thighs spring back to the touch, 5 to 6 minutes per side. An instant-read thermometer inserted into the center should read at least 155 degrees F (68 degrees C). Slice and serve with the dipping sauce.