In a medium bowl, stir together the olive oil, ranch dressing, Worcestershire sauce, rosemary, salt, lemon juice, white vinegar, pepper, and sugar. Let stand for 5 minutes.
Pound, chicken breast to 1/4" thickness. Place chicken in the gallon size Ziploc bag, and stir to coat with the marinade. Cover and refrigerate for at least 8 hours
(all day). Preheat the grill for medium-high heat. Grill chicken for 8 to 12 minutes, or until the chicken is no longer pink in the center, and the juices run clear.