Peel and devein the shrimp, leaving the tails intact. Combine the grapefruit juice, orange juice, lime juice, cilantro, mint, salt and pepper in a shallow glass dish. Add the shrimp and toss well. Marinate, covered in the refrigerator for 30 minutes. Drain the shrimp, discarding the marinade.
Arrange the shrimp evenly on 4 metal skewers. Spray the grill rack with nonstick cooking spray. Place the skewers of shrimp on the grill rack. Grill, with the grill lid down, over medium-hot (350 to 400 degrees) coals for 3 minutes per side or until the shrimp turn pink. Serve over hot cooked rice.