1 quart lime sherbet
1 (2 liter) bottle diet lemon-lime carbonated beverage
Place sherbet in a microwave-safe bowl; heat in microwave until slightly melted, about 10 seconds.
Stir lemon-lime beverage, about 1/2 cup at a time, into sherbet until punch is the texture of a milkshake. Pour punch into a large punch bowl. Slowly stir the remaining lemon-lime beverage into punch.