To be a back seat driver means to censure or disapprove somebody or something not directly but from behind, generally giving an opinion or advising needlessly. It is like the passenger sitting in the back seat of a vehicle and giving unwanted advice to the driver.
1. Varsha was a new employee and was not aware of some of the company policies. Nevertheless she always behaved like a back seat driver during the weekly meetings.
2. The physiotherapist always behaved like a backseat driver when the Surgeon was advising his patients.