AKA Shnuk and Shnukel
Yiddish for "an easily persuaded customer", AKA a sucker. It is sometimes used to refer to any stupid or insignificant person.
It first appeared in written English in 1948, but was no doubt used in spoken language well before that. We don't know exactly where it cam from; most likely it comes from the Yiddish shnuk (pronounced the same), which was used to mean a fool; it is said that the literal meaning is actually 'elephant's trunk', although it is unclear why these two ideas would be related. It is also possible that it comes from either the Yiddish schmuck, meaning 'penis' or the German schnucke, meaning 'a small sheep'. It has fallen out of common usage, and is rarely heard any more.