To a bowl add the garlic, oregano, salt, parsley, and crushed red pepper, if adding.
Add lemon juice (or vinegar) and olive oil. Whisk aggressively and give it a taste. Add more salt, as needed.
Add the chicken to a sealing bag or shallow dish, add the marinade and mix well. Be sure the chicken is submerged in the marinated. Cover if in a dish. If in a bag, place into another container in case it leaks.
For best flavor refrigerate the chicken overnight. At a minimum, try to marinate for at least 4 hours.
Heat the grill to medium-high heat. Grill the chicken for approximately 8-10 minutes per side. Grill the chicken thighs until nicely charred. You are looking for an internal temperature of 165ºF.