A 'grasshopper' refers to a distasteful male or female - usually someone ugly, usually always stupid and annoying. The term is most commonly used when you are out in a social situation and somebody awful won't leave you alone. There is a hand gesture to accompany the term, which consists of you using the pointer finger of each hand to imitate antenni.
*Two attractive females are at a popular bar, minding their own business. An awful man approaches them, inisisting that they dance with him, and eventually leaves, after tireless refusals from the females.*
Sarah: Wow. That guy just wouldn't leave us alone.
Steph: I know. What a grasshopper.
*Two attractive females watch as an extremely unfortunate looking, drunk woman cracks onto some attractive men. The females then go and save the males from this drunk woman*
Steph: Woah. What a grasshopper.
Sarah: She is a grasshopper for sure.
Male: Definite grasshopper.
Male 2: Thanks for saving us from that grasshopper.