Is there an English idiom for Bengali idiom "সবজান্তা গামছাওয়ালা"(wise towelsman)?

In English, we have the infamous know-it-all: one who knows everything; hence, a person who makes pretension to great knowledge, especially one whose didactic conversational habit conspicuously reveals his belief that he has superior knowledge on many subjects; a wiseacre; a know-all; -- usually ironical. [Colloq. & pejorative] Note: the use of this term implies that the speaker disapproves of this behavior, and may think that it is unjustified.

**know all: someone who seems to know everything and annoys other people by showing how clever they are.

No one likes him because he's such a know-all.

smarty-pants is an older idiom, for one who is obnoxiously self-assertive and arrogant, as is weisenheimer.

There is the Jerkass, who might say something like, "Sometimes I park in handicapped spaces while handicapped people make handicapped faces. I'm an asshole!" (— Denis Leary, Asshole) but this is more trope or jargon.

And, as StoneyB has kindly reminded me, there is the loudmouth:

Be loquacious, often noisily or boastfully; someone who talks too much or too loudly, esp. in an offensive or stupid way

*Harvard Square: Know-it-all capital of the universe. * - Universal Hub.

I cannot call any fixed phrase to mind, but the role is familiar in American literature. In small towns it is traditionally associated with the barber or hairdresser, and in big cities with the cabdriver—no doubt because in their professions they have captive audiences.

The bartender is a related figure, but tends to be seen rather as a source of genuine wisdom, albeit of a dark and sardonic cast.

In Eastern European Jewish tradition (carried over into American Jewish culture) there are stories of the Wise Men of Chelm, a mythical town populated by fools. The inhabitants were renowned for their clever advice, none of which made sense. For example:

A man dug a well, but didn't know what to do with the dirt from the hole. He cleverly decided to dig another hole and dumped the dirt in. But now he had a new pile of dirt.

Being wise, he realized if he dug another hole, he would still have the same problem. So he consulted the Wise Men of the village who came up with a brilliant answer: Dig a new hole twice as large.

There is a similar English tradition of Gotham, which was also populated by wise men.

Washington Irving is credited with attaching the term Gotham to New York City based on the obvious wisdom of its inhabitants.

Someone who expresses opinions on subjects beyond the scope of their expertise is also called an ultracrepidarian

adjective

1. noting or pertaining to a person who criticizes, judges, or gives advice outside the area of his or her expertise: The play provides a classic, simplistic portrayal of an ultracrepidarian mother-in-law.

noun

2. an ultracrepidarian person.

The rather charming story of the origin of the word (which literally refers to "beyond the sandal") can be found on wordsmith.org (and many other places):

The story goes that in ancient Greece there was a renowned painter named Apelles who used to display his paintings and hide behind them to listen to the comments. Once a cobbler pointed out that the sole of the shoe was not painted correctly. Apelles fixed it and encouraged by this the cobbler began offering comments about other parts of the painting. At this point the painter cut him off with “Ne sutor ultra crepidam” meaning “Shoemaker, not above the sandal” or one should stick to one’s area of expertise.

Addition: The story was told by the Roman writer Pliny the Elder, hence Latin.