Place olive oil, lime juice, onion, tarragon, salt, and hot sauce into a large, resealable plastic bag; shake to mix. Add chicken thighs, coat with marinade, squeeze out air, and refrigerate for at least 4 hours.
Preheat an outdoor grill for medium heat and lightly oil grate. Remove chicken from marinade, and shake off excess. Discard remaining marinade. Season with salt and pepper.
Grill chicken for about 30 minutes, or until no longer pink in the center. Chicken thighs don't dry out easily, so don't be afraid to cook them a bit longer if needed.