A schmuck is a loser, idiot, or jerk. This Yiddish word is a little old-fashioned and not very harsh.
If you've ever felt like a dummy or sucker, you've felt like a schmuck. This is one of many Yiddish words for "jerk" or "idiot" that are common in English, including schmo, schlub, schlemiel, and schnook. Old-fashioned and kind of unusual, schmuck is probably one of the least mean ways to call someone a loser.
