A male or female that is stingy, lives off other people mainly hence they wait for crumbs (opportunities) to come to them. They are a common breed and display traits of being "loose" or just a plain loser.
Other slang: Snackratacus (ultimate snack rat)
Dude you shouldn't hook up with her, she's a total snack rat.
Man, he didn't even pay for anything this weekend..I think we just got snack rated by king snackratacus