It is the word used in a play. The paragraph in which it is stated is the following:
Why does everybody sabotage me, Frank? I give work, I pay
well, yes ? They eat what they want, don’t they ? I don’t
know what more to give a man. He works, he eats, I give
him money. This is life, isn’t it? I haven’t made a mistake,
have I ? I live in the right world, don’t I ?
you’ve stopped this world. A shnip! A boy! You’ve stopped
it. Well why? Maybe you can tell me something I
don’t know —just tell me.
What I’ve found is that this word can be used in place of any word we don’t remember. I personally guess it’s something like "you little piece of shit" in this context.
Can anybody tell me the equivalent?
By the way, Peter is German. Is it possible that the word refers to that?
It is Yiddish, and means an insignificant person:
Green’s Dictionary of Slang
an insignificant person.