Basically when south dropped out of the Nsl, oakleigh tried to be "hellas lite", in addition of having a transfer policy which was basically sign anyone that had played for hellas in the Nsl, they also tried to poach south players year in year out, see back in 2005/2006/2007 etc south were still in a precarious position financially, and oakleigh tried to run us into the ground every off season, apparently the 2 clubs had made a gentlemens agreement that the 2 clubs would not try and sign the others players, oakleigh broke that deal and would basically target any of our decent players and in many cases succeeded, add the fact that a lot of oakleighs board were south backers in the Nsl and the people who claim to follow them were hellatzides in the Nsl, hatred started to naturally grow and we would always be subjected to taunts of "hellas is dead" etc from them. In 2006 oakleigh would finish top of the table with a records point tally, only for hellas to win the grand final, and then it just became an obsession for them, when they beat us last year they had a pitch invasion like they won the title, the funny thing is they have never won anything, south yet again pipped them to the title last year, and once again today we put them in their place. Today they had ex a league players like kofi danning (Brisbane roar) matthew foschini ( victory), sean Rooney (newcastle jets) and Mirjan Pavlovic (Wellington phoenix) in their starting 11 and we still thumped them, the burn that club continues to feel every time we lift silverware is hilarious.
As far as the rest go Heidelberg is the Nsl rival, they don't like us, we don't like them, but a mutual respect does exist, it's the only true rivalry that means something, bentleigh is a small rivalry but nothing major I wouldn't say theirs a hatred between the clubs, they have a bit of oakleigh about them but aren't as vocal, western suburbs is like a sister club to south melbourne and the clubs have always been on good terms, in fact I think south tends to get along most with the greek clubs from melbourne's west, where as from the south east it's more your ex hellas types turned melb victory that just want south to lose.
This is why Sydney Olympic is so lucky that they have the greek market just for themselves, we go head to head with greek clubs almost every fortnight and for them it's treated like a grand final, honestly not even the Turks kill themselves to try and beat us like the greek clubs do, this is why when south win cups and titles it shouldn't be taken for granted, it's harder to win stuff now then what it was in the Nsl days!