A grasshopper is a sweet, mint-flavored, after-dinner drink. The name of the drink is derived from its green color, which is provided by the crème de menthe. The drink reputedly originated at Tujague's, a landmark bar in the French Quarter of New Orleans, Louisiana, and gained popularity during the 1950s and 1960s throughout the American South.
Penny made Raj his first one and he has been drinking them ever since.
In "The Grasshopper Experiment", Raj is introduced to alcohol and the Grasshopper cocktail. He find that the drink allows him to steer around his selective mutism and talk to Penny and other women. Unfortunately, he is somewhat misogynistic as a drunk.
In "The Stag Convergence", Raj is drinking Grasshoppers during the toasts. "This grasshopper is kicking my ass hopper!"