Nockers are capable of cursing in contemporary language and the other kithain certainly know this. Frustration can run so high at times, though, that common language falls short of letting nockers express their emotions completely. That's when they break into what sounds like gibberish to anyone else hearing them but is in fact a complex language that evolved strictly for the purpose of venting. Not even the they understand the letter of it but the inflections and combinations of sound allow them an intuitive grasp of what other nockers are cursing even if it can't be translated into the local tongue.
Amazingly enough, even this language has its limits. Few nockers ever reach the level of frustration that surpasses the language, though, as frequent outbursts keep them from hitting the boiling point.
One infamous curse was uttered in nocker history, though, and it became a word of power. It was actually more a string of heart-stopping insults than an invocation. This profanity escaped from the original Basilisk Stone when it shattered and it penetrated like a 10-penny nail into the subconscious of every Nocker. Because of this, it is not accessible to the conscious mind: it can't be remembered (by nockers or anyone who hears it) and can't be said on command. It's more likely to be blurted out under times of extreme stress and frustration... like when an invention that's been under years of construction suddenly falls apart or a Redcap decides to eat him or her anyway despite the cacafuego they'll get later.
In game terms, the storyteller decides when the Nocker utters this invocation. The player spends a point of Glamour when its spoken. Every non-nocker hearing it suffers an amount of chimerical damage equal to the nocker's Glamour pool (before spending the point). Armor is no protection and it cannot be soaked.
An interesting side effect of this mother of all curses is that anyone who hears it swears like a Nocker for hours afterward. No effort short of spending a Willpower point or being struck mute can keep them from swearing.