proper slag
Not just a normal slag willing to sleep with any old John, dick and Harry. A 'proper' slag exudes an air of utter filthiness when viewed from a distance. When up close and personal she'll service your every need : swallowing and anal is guaranteed. When you see one you know it, nuff said.
Never mind your slag, that over there is a proper slag - I'm gonna rag the Fuck out of that one.