When I leave them lying in their pool of blood, tears, vomit and excrement, begging for forgiveness over questioning my supreme judgment!
No seriously, it's not an exact science nor can you always "win", for more reasons than one, nor is it even about any sort of "victory". There are generally two goals in an argument, either to get your "opponent" to understand your point or view or to accept it as his own. The latter is generally... wrong as, barring a few matters, different opinions on a single matter are most often valid, especially when it boils down to choice and preference, as a lot of (casual) debates often do.
If someone says "I understand what you mean, but" that's generally enough for me. I like debating, not for the sake of forcing my own opinions on people, but just because I'm argumentative by nature and simply enjoy a good debate and I like seeing how other people think (not just what, but how, the process is far more interesting than the content in most cases for me)