A couple of times I've seen a phrase much like "that's horrible coding — and I would know from horrible coding!" This seems extremely peculiar to me (if only because of how ungrammatical it is), and while I can guess that it's supposed to be some emphatic way to indicate the subject's authority on the matter, it's pretty unusual and I don't fully grasp it.
Unfortunately, I don't have a good verbatim example on hand, so it's possible my memory is muddling the context of the phrase slightly.
Anyway, what does this bizarre turn of phrase mean exactly and where does it come from?
Best Answer
Evidently, the phrasing arose as a result of literal translations of certain phrases from Yiddish to English. Fred Kogos, From Shmear to Eternity: The Only Book of Yiddish You'll Ever Need (2006) identifies two such Yiddish phrases followed by their idiomatic and/or literal English meanings:
and
The form appears in Yiddish-inflected speech (and writing) such as this extract from Writers Forum, issues 21–23 (1995) [combined snippets]:
And from this point of entry, the structure extends more broadly into non-Yiddish English. From J. Brent Bill & Beth A. Booram, Awaken Your Senses: Exercises for Exploring the Wonder of God (2011):
Lilliam Feinsilver, The Taste of Yiddish (1980) has this entry for "know from" [combined snippets]:
FOLLOW-UP (January 8, 2015):
I just came across this discussion of "know from" in Leo Rosten, Hooray for Yiddish! (1982):
Rosten's comment strongly supports StoneyB's comment beneath the OP's question above that "know from" is an old New York Yiddishism that now functions primarily as "an ironic emphatic."