a person usually who has just crossed the border by hopping a fence or digging a long underground tunnel. most like mexican or some form of hispanic spic. these are the people who work for 50 cents an hour either landscaping or picking fruit hence the name "melon picker". most melon pickers never bother to learn english but instead make america adjust to their way of life.
the person blowing leaves in your neighborhood park who whether you tell them to keep going or stop will say
"ahhh si senor" and blow leaves at you. then you can call them a goddamn melon picker