Peel and devein shrimp, if desired, and set aside.
Cook noodles in boiling water 3 to 4 minutes; drain.
Saute garlic in hot vegetable oil in a large nonstick skillet over medium heat 2 minutes. Add shrimp, and cook 2 minutes or just until shrimp turn pink. Add beaten egg to shrimp mixture in skillet. Cook shrimp mixture over medium heat, without stirring, until egg begins to set. Stir until cooked, breaking up egg.
Add sugar, fish sauce, and garlic-chili sauce, stirring until blended. Add noodles, and cook 1 minute or until thoroughly heated. Sprinkle with onions, peanuts, and cilantro. Squeeze lime wedges over noodles, if desired.
*Thai rice noodles may be found in the Asian sections of larger grocery stores or at Asian markets.