Is there an idiom in English to describe someone who thinks he/she is smarter/wiser than everyone else?
In Polish, we have an idiom, which literally translated, would sound like:
He/she has eaten all minds
In English, a common term for such a person is "know-it-all", as in:
Ever since Bob took that first-year philosophy course, he's acting like such a know-it-all.
Usually the phrase has a slightly negative connotation to it, because it implies that the person really doesn't know it all, but they might act arrogant as if they do know it all.
There are numerous amusing English terms for such a person, including
• wiseacre (“One who feigns knowledge or cleverness; an insolent upstart”),
• smarty-pants (“A smart aleck or know-it-all”),
• clever dick (“(chiefly UK) A person who annoyingly tries too hard to impress with their cleverness”),
• smart aleck (“One who is pretentious about their own cleverness or knowledge; a know-it-all”, but also with senses “One who is obnoxiously self-assured; a show off” and “One who is given to obnoxious or insolent humor; a wise guy”).
Some terms related to the above, but with slightly different meanings, include
• wiseass (“One who makes wisecracks, particularly in a sassy or cocky fashion”),
• smartass (“(slang) One who is particularly insolent, who tends to make snide remarks or jokes”).
Focusing on the wiser aspect:
Characterized by an attitude of moral superiority