The Yiddish term khoyzek refers a "mockery" of something else. According to Dov Sadan (cited here) this word derives from Khoyzek a demon in Jewish folklore. I looked high and low and could not find any evidence of a demon name Khoyzek in any Jewish (or even non-Jewish sources). Does anybody know of any sources which mention such a demon?
Sadan's article is discussed in depth here.
Yiddish is a thousand-year-old Jewish language, with origins, according to a broad scholarly consensus, in the German Rhineland. The major component of Yiddish, in both its Western and Eastern varieties, is Middle High German, with varying admixtures of Slavic, Hebrew, and other languages. There are many words that clearly have a Hebrew origin in Yiddish, like meylekh (“king”), azes (“brazenness”), kheyshek (“desire”), menukhe (“rest”), metsiye (“bargain”), sod (“secret”), tomer (“whether”), miyes (“ugly”), yakres (“expensiveness”), nakhes (“satisfaction”), shoyte (“fool”), kol (“sound”), mishpokhe (“family”), tsure (“face”), etc.
The origin of Khoyzek in Eastern Yiddish, pronounced chausek in Western Yiddish, is unclear.
Much of the confusion stems from an old theory, which states that khoyzen derives from cheisik, a word first mentioned in Philoglottus with the German meaning belustigung, meaning "amusement". Hans Peter Althaus translates Belustigung as (in Hebrew letters)
which also renders cheisik according to the Yiddish dialect dictionary.
A more modern theory links khoyzek with modern Eastern Yiddish kheyshek (lust).
Note that both theories revolve around German translations that contain "lust", from Middle High German lust, from Old High German lust, from Proto-Germanic lustuz. Cognate with English lust, West Frisian lust, Dutch lust. Interestingly, lust etymologically can mean both pleasure and desire, the latter for example in the Yiddish expression:
Isch wil un hob cheischek. ‘I want it because I want it.’
However, we also have this Yiddhish idiom, which suggests the origin of the word may be Germanic:
Versmakht khoyzek oys dir, dem zol onvaksn a khoyzek oyf der noz
which in modern German would render something like:
Wer macht khoyzek aus dir, dem zoll anwachsen eine khoyzek auf der nase
He who makes fun (khoyzek) of you, let a khoyzek grow on his nose
This makes absolutely no sense, unless you take into account that the older Yiddish form of the word is *chausek meaning "fortress". Now the German word for "fortress" is schlosz, which can also refer to female genitals. Interestingly, there is also a link with "nose" in German:
schlosz nennt man auch an den pferden das ende der nase (schlosz is also the name for the nose-bridge of horses)
So clearly the idiom is wordplay on the different meanings of khoyzek.
It is with this consideration that we can identify the origin of the "demon" association, which starts with Jeremiah 20:7
Thou hast persuaded me, O Jehovah, and I am persuaded; Thou hast hardened me, and dost prevail, I have been for a laughter all the day, Every one is mocking at me,
The link is "everyone is mocking at me". The Dead Sea Scrolls version of the text of Jeremiah quotes some of Jubilees where שעירים (se'irim) may have been the Hebrew word in Jub 1:11, which was then rendered in Ethiopic Jubilees as demons.
Se'īrīm are frequently compared with the shedim of Hebrew tradition, along with satyrs of Greek mythology and jinn of Arab culture
For an in-depth explanation, see Tigchelaar's Jeremiah’s Scriptures in the Dead Sea Scrolls