In the Bengali language there is an idiom, "sobjanta gamchawala" (wise towelsman), meaning a man whose occupation is merely to sell towels, but claims to know everything and gives valuable advice on any and every topic.
As you can imagine, wise and valuable are used here as sarcasm. In Bengali, the phrase is used to point out a person who always makes a comment on every topic without knowing the context.
Is there is an English idiom or phrase for that?
I'm not looking for jack of all trades is a master of none. A jack of all trades is able to do a lot of things fairly well, but sobjanta gamchawala isn't.