Armchair quarterbacks is a popular idiom used to describe people who criticize or offer unsolicited advice about a situation or decision, but have never been in the position to do so themselves. Here are some synonyms for the expression: couch coaches, desk jockeys, keyboard warriors, Monday morning quarterbacks, sideline spectators, armchair generals, and backseat drivers. These phrases are commonly used to describe someone who is giving their input without being actively involved or having any practical experience. It's essential to be cautious when using these idioms as they can be perceived as derogatory and dismissive towards someone's opinions and expertise.