A slapper is a girl or woman that in earlier era's would have been called a nymphomaniac. The true slapper would shag anyone and anything if it just meant she could satisfy the craving for sexual fulfilment for 10 minutes. The word is used as an insult and a reminder that the woman is the type that loves a big pair of balls slapping against her arse - hence the term "slap and tickle" - a slapper is a woman that likes a lot of slap and tickle
What a fuckin slapper tho man, I bet she likes a good thick end up the knicker leg.
Eh mate she's a right slapper - you wear some protection and while youre on the job give her one for me cuz I wouldnt touch her with a barge pole - just stop and say "by the way this ones for steve"