1. An individual who cares not for relationships beyond the realm of the sexual, these people sleep with many partners not caring about anything save for the moment of climax.
2. Rubbish that is not worth the time or effort of paying attention to it, but none the less draws one in. Used to describe unpleasent situations.
3. Physical trash, often scrap metals.
4. Drawn from frag, to slag something is to destroy it, used in cases of technological rather then biological items.
So your wife's been a nasty slag all along? I knew she was trouble from the moment I first laid her.