You're not S if you only specialise in one build or one powerful skill. If there's even a single skill in your class' tree that you can't summarise and list the applications of (including good combos for active skills, and quirks like on-hit effects) from the top of your head, you can't claim to have "mastered" it.
You're not S if you don't know how your class functions in different environments, e.g. PvM vs PvP vs GvG, and can't discuss viability in those environments without referencing someone else's work. Pros, cons and caveats. If you can't provide your own examples or calculate things for yourself, you haven't mastered your class.
You're not S just because you deal lots of damage, have fancy gear, or a nice build. You could have easily just geared from an all-purpose guide in the class subforums or gotten someone to tailor a build for you. Having lots of zeny to burn and access to a plethora of information complied by other people =/= being skilled with your class.
You're not S if you can't see what a piece of gear will do for your class by looking at its effects. This goes doubly for the people who ask what effects base stats have on specific skills. Pretty self-explanatory.
You're not S if you look at a local vid (not from another server) of someone playing your class and can't immediately deconstruct what's happening, how they're moving the way they are, or dealing the kind of damage they are. If anything about someone else playing your class baffles you, then you haven't mastered it. If you get confused about things like gear swapping to cancel actives, hitlocking, intentional posbugging or skill dancing, then you haven't even come to grips with basic game mechanics let alone your class.
Finally, if you believe your class is unequivocally the best in the game at everything and can't find a single fault with them (hello Ranger mains):
Sorry, but it's getting really annoying seeing people rate themselves S when they clearly have no idea what they're on about.
