> Monday morning quarterback: A person who analyzes the mistakes they made they day after they've made them. Derived from complaining over quarterbacks on monday morning after the sunday game. [0]

[0]: http://www.urbandictionary.com/define.php?term=monday%20morn...

People who watch a football game Sunday night and then talk shit at work on Monday about all the things they would have done differently if they were coach/quarterback/etc.

Might have something to do with this[0]

>The definition of a Monday morning quarterback is someone who is always criticizing and saying how he would have done something better or differently after the event has passed.

[0] http://www.yourdictionary.com/monday-morning-quarterback

It's a polite way of calling someone a know-it-all.

Same meaning as hindsight is 20/20.