Adding a "Shm" to the beginning of a word is meant to diminish, negate, or dismiss an argument (for instance, "Rain, shmain, we've got a game to play").
It can also indicate that the speaker is being ironic or sarcastic.
This process was adapted in English from the use of the "schm" prefix in Yiddish to dismiss something; as in, "sale, schmale" (thus denying that the sale is worthwhile).
While "schmo" ("schmoo", "schmoe") is thought by some linguists to be a clipping of Yiddish שמוק "schmuck",[1] that derivation is disputed.
[2] This name-related article is a stub.