The Jargon File (version 4.4.7, 29 Dec 2003):

frotz
 /frots/

    1. n. See frobnitz.

    2. mumble frotz: An interjection of mildest disgust. The word ?frotzen? is
    live in this sense in some eastern German dialects; the safe bet is that it
    came to hackers via Yiddish.