Seafood extender
The kind of unattractive person who doesn't qualify as being a prawn. Whereas with a prawn you keep the body and throw away the head, with seafood extender you throw away the lot.
Steve: "That chick I picked up last night was a bit of a prawn"
Mark: "Really, I thought she was more like seafood extender"
Mark: "Really, I thought she was more like seafood extender"