Why do yiddish people put schm- in front of a word?

Answer 1

The people who put schm- in front of a word are not the Yiddish speakers.

They are generally those non-Yiddish speakers who are at the same time

intellectually challenged and trying to effect their impression of Yiddish

speakers, often for comic effect. They usually come off as crude and in

poor taste.

They also typically develop instantaneous linguistic amnesia regarding smack,

smell, smoke, smog, smooth, smooch, smother, smoulder, smudge, smuggle,

smug, smurf, and smut, none of which are Yiddish words, not to mention

smegma, which is a totally non-Yiddish problem.

Answer 2

In Yiddish, adding "schm-" to a word is a way to add emphasis or to convey sarcasm or disbelief. It is used to create a playful or mocking tone in conversation.