1. Mix the cider vinegar, mustard, crushed garlic, lime and lemon juice, sugar, salt and pepper in a bowl. Whisk in the oil.
2. Place chicken in the mixture, cover and marinate for 8 hours, or overnight.
3. Preheat the BBQ and place chicken on a lightly oiled grate. Cook for 6 - 8 minutes per side, until juices run clear. (Check this by inserting a thermometer into the thickest part of the meat - when the temperature reaches 165F or 75C, it is cooked.)
4. Discard the marinade.