According to Kevin Smith and Jason Mewes the origin is this: When Jason was younger, about 14, he used the "nee"-expression as a means of countering a statement just made, as in "I'm gonna fuck your mom tonight - nee". The "nee"-expression then grew and grew, but always refering to the canellation of "charge" in a statement. Thus, snoogans means to not do anything. Just the same as Wayne's world's "not!"-expression. Of course the snoogans works excellent as a stand alone-expression, but the "true" ethymology is the one stated above.
I'm so gonna own your sisters pussy, snoogans