A girl that is only good for sex, usually overweight. A fat or 'rubinesque' booty call. Similar to a 'moped' but more specific.
"Man, look at her scarf that burger. I bet she could eat a mean cock, she'd make a perfect Fuckpig."
"I was going over to Hillary's but she bailed. Instead I called my Fuckpig and she's coming over to pick me up."