An insult hurled at new zealanders, by australians mostly. it is a reference to the sheep prominence in new zealand- ten sheep to every person. sheep cant breed that fast on their own, so the "sheep shaggers" help
Kiwi: we fucked you aussie's up in the rugby union!!
Aussie: go fuck a sheep, ya sheep shagger.
Kiwi: leave my mutton out of this...