It can’t be, though. In German it is spelled Schwanz, with a capital S. “Shvants” looks like an attempt by an English speaker to transliterate that word. But any Yiddish speaker would write it exclusively as " שװאַנץ", unless they were writing High German, which case we have covered. I do not envision a scenario where they would spell it like an English speaker illiterate in both German and Yiddish, though while I know German and Hebrew I don’t know from Yiddish so I can’t be absolutely 100% sure.
And here is where I notice that both Hebrew and Cyrillic have a letter for the “sch” sound, and that the two letters bear an obvious relation to each other.
But, usually, a cigar is just a cigar.
Which is perfectly OK for an English-language message board.
Which is an entirely reasonable course to take in a casual discussion on an English-language messageboard about dialogue in a comedy movie. Although I realize that said messageboard regards nitpicking as a religious requirement. 
BTW “Stecker” means “plug”, from stecken, to stick. “Stück” is a different word.
You will get no argument from me.
Which is what I said: ‘Stück (pl. Stücke) means “piece”.’ 
Didn’t know Stecker.
Kind of surprised it hasn’t been noted that “penis” itself is Latin for “tail”.
Okay. Yiddish is mostly German formally written in Hebrew characters. There are sounds in Hebrew or Yiddish that are NOT in English or the Roman alphabet we English speakers use. So transliterating Hebrew and Yiddish into English, well, there are NO standard spellings. Then take into account those of my grandmother’s generation were immigrants from central Europe where Yiddish was their mother tongue and English was their second language (or third or forth … there was Hebrew and maybe Russian or Polish).
The point I wanted to get to is Ws and Vs sorta got confuddled when they were speaking English or Yinglish. Where native English speakers would read “Schwantz” and say “schwantz”, German and Yiddish speakers would say “Schvantz”. And Schwantz, along with Schmuck, Putz, Schmekel, Schmekele,
and Petzele are all references to a Penis. *
Shtup is Yiddish for the act of sexual intercourse. It seems I tossed in an extra C in the OP. So sue me.
As for the movie? Teri Garr, as lovely as she is, as talented as an actor as she is, is a Shiksa and Brooks let her mispronunciation slide.
- don’t get me started on the endings I think of as an “affectionate diminutive”.
Or, you could be totally wrong. For that matter, who knows who wrote that line? Could have been Gene for all we know.
“Totally wrong” about what?
You have to be kidding if you think anyone but Brooks made up the word.
Prove it! 
Mel did not write that line. Gene did. Check the First Draft screenplay:
INGA
(pointing to another
paragraph)
And look at this, Doctor!
FREDDY
(reading)
'Dilation of his sacral
parasympathetic impulses would
cause an increase in flow of
blood and the erection to
approximately nineteen inches
of his apparatus genitals.’
IGOR
His what??
INGA
His schwanzstucker.
IGOR
Whew! A nineteen-inch drill.
I assumed the point was to give a reason why the word for “tail” would also mean “penis.” It makes sense that the latter evolved because the penis is like a man’s front tail. It probably started out as a euphemism, similar to the English “cock.”
Wow, I’m glad they changed that first draft, because what made it in was much funnier.
Though that might just be Garr’s delivery.