‘So, Adam, you have the privilege of being my first Seppo.’ ‘Your first what?’ ‘Seppo. You′ve gotta learn to speak Aussie, man. You′re a Yank, so –’ ‘No, not a Yankee. I′m from –’ ‘The You Ess Ay. Makes you a Yank. Yank rhymes with septic tank. But we like to shorten names and then add an O at the end - but only if we like you. So Yank is kind of neutral. Septic tank is rude. But Seppo, well, it′s affectionate. Get it?’ ‘No.’
Source: wiktionary