A Backseat Driver is someone who gives unwanted and unneeded advice, and sometimes also criticism. A Backseat Driver usually interfers in affairs without having the authority and knowledge to do so.
Example of use: “Daisy is such a backseat driver, she needs to stop interfering – no one asked for her advice.”
“Jake tries to sound like an authority on the subject but he’s actually a backseat driver.”
The term 'Backseat driver' (sometimes also spelled 'back seat driver') originated in the United States in the early 1920s. This happened as transportation via automobiles became more common, and wealthy people started using a private chauffeur who sat in the driving seat and got the directions from the person in the back seat. The first recorded figurative use of the term was in the 1921 December edition of the Bismarck Tribune: "A backseat driver is the pest who sits on the rear cushions of a motor car and tells the driver what to do..."