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1.
Female companion which is often phoned to meet up for casual sex when drunk or (lagging)...

The Lag Slag is often lacking in attractiveness and happy oblige as she is doesn't often get laid.

No means of contact is then made to the lag slag until you are lagging again.
Q.What did you do last night bruv?

A. Got pissed up and met my Lag slag..
by George a Johnson June 16, 2007