Schmuck is a name for someone who is mean, foolish, or inept. Synonyms include jerk and idiot. There is a pejorative connotation to the term. The plural is schmucks.
Putz is even less formal than schmuck. Putz can be either a noun or a verb. As a noun it describes a person as foolish or without value, usually someone who does not contribute to society or a family. The plural is putzes.
As a verb, it is the action of doing things that are time consuming without being worthwhile. In other words, activities that a putz would do.
Even though they don’t seem similar, putz and schmuck share the same meaning in Yiddish. Schmuck comes from shmok meaning penis. And putz comes from putz, which is another word for penis.
These terms are informal and could even be called slang. They should not be used in formal writing.
While Tom looked torn throughout the performance, and later admitted he was a “schmuck” for not snapping up the Pengam Green performer, both Rita Ora and Ricky Wilson looked stunned she had not been selected. [Wales Online]
Meanwhile, the poor schmucks who bought shares on the public exchanges often got left holding the bag when the companies went bust. [Fusion]
If someone has deep admiration for one person, and that one person winds up being a putz, the effect will be far more devastating. [Chicago Now]
If there were no billion TV deals, or all the free advertising that papers and websites provide, if there were no pocket-lining endorsement deals made possible only because of the media, Lynch and those like him would not be making so much money that they can eat a six-figure fine for being post-game putzes. [Toronto Star]