Use scissors to remove shells without disturbing tails. In a glass bowl or food storage bag, combine crushed garlic, salt, lemon juice, and olive oil. Put shrimp in bowl; stir to coat well. Cover and refrigerate for 2 hours. Thread marinated shrimp onto skewers and grill 5 to 6 inches from coals for about 12 to 15 minutes, turning frequently.
If broiling, remove tails.
Serve shrimp with garlic butter, for dipping.
In a small saucepan, melt butter; add remaining ingredients. Heat through and serve with the grilled shrimp or other seafood.