Going South is apparently poker slang for ratholing, that is, taking chips off the table once you've won a big pot (in order to "guarantee a win" by ensuring you cannot lose the money you remove).
In season one of High Stakes Poker, Johnny Chan and Sam Farha joke about Freddy Deeb "going south" when Freddy leaves the table to use the bathroom. Daniel Negreanu seemed to not be paying very much attention until it got a bit loud, and apparently thought that Johnny and Sam might be serious. When Freddy returns, Daniel Negreanu asks Freddy if he went south. Freddy, not believing that anyone could be asking him that, at first laughs it off, but then the realization begins to sink in: one of his fellow players has just asked if he was cheating.
Freddy considers himself a very honorable player (as all high stakes players must), and takes offense at the comment. When no one will seem to own up as being the person who started the accusation, and others say "just laugh it off", Freddy gets angrier and angrier, finally calling a halt to the entire game and demanding that the floorman be brought in to mediate. Eventually, Freddy calms down and the game continues, but no one ever admits to Freddy what exactly was said and who said it.
Freddy strenuously denied ratholing, and since the show was televised, the on-air commentators (Gabe Kaplan and A.J. Benza) made a point of saying they checked the replay and the tape, and Freddy did not take any money off the table. To do so would have been dishonorable and against the rules of the game, and to accuse another player of doing so was quite insulting.
There is a technial difference between "Rat Holing" and "Going South". Rat holing is cashing out from a table and returning to the table with a buy-in that is smaller than the ammount that was cashed out. Going south is taking chips off the table and puting them in your pocket so that they are not in play but the player did not cash out.