Che cosa, Cusamano?

I've been wending my way through the first season of The Sopranos, which is wonderful not only for the stellar performances by the entire cast, but for the complexity of its writing. The Sopranos' writers withhold such a wealth of information as to intentions, motivations, and even the meaning of words that watching each episode requires one's utmost attention. One particularly confusing feature of the last episode I watched, "A Hit is a Hit," was the use of the word "cus," a nickname for a character with the last name of Cusamano. The character alludes to the fact that, in Italian, the word "cus" bears a negative connotation, but does not elaborate on the meaning. The writers deny the audience a chance to understand the full meaning of the word, which I can only hope will be explained in a later episode. Even drawing on the wealth of information now available through the internet, I was unable to find a hint as to the meaning of the phrase.