Synonyms (see below) include the bee's knees, the cat's pyjamas, or, strangely enough, the cat's arse.
Look at that pony-tailed wanker in his BMW. He thinks he's the ducks guts.
Famously used in the 1979 Australian Film 'Mad Max'
Goose; "You can shut the gate on this one Maxxie, Its the Ducks Guts!"