I heard this ages ago and thought you'd all like to hear it.
In a match between Aus. and Zimbabwe, Glenn McGrath was bowling to Daniel Vettori. After his follow-through, McGrath said to him "Why are you so fat?". After his next delivery, Vettori replied "Well, every time I sleep with your wife she gives me a biscuit!". Adam Gilchrist, who was listening to all this from behind the stumps, was then seen rolling around on his back in a fit of giggles
That just proves that the Aussies' sledging does backfire (occasionally!)!