I have a friend that would consistently say, "I could have told you that," only after the fact is said.
But when I test him before the fact is revealed, he wouldn't know the answer. He has narcissistic traits.
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A person who talks at length but says little of any value:
'I think he’s a pompous old windbag'
(Especially in children’s use) a person who copies another’s behaviour, dress, or ideas:
'all writers are copycats'
Mr.Know it all.. (its a sarcastic way to refer a person who acts as though he/she knows everything) check this for reference.
Sounds like a Monday-morning quarterback to me:
a person who criticizes the actions or decisions of others after the fact, using hindsight to assess situations and specify alternative solutions. [dictionary.com]
You could call a person like that Captain Hindsight:-
A stupid ass superhero from the South Park episode Coon 2: Hindsight. He flies around the world providing hindsight after every catastrophy that happens, but doesn't actually do anything helpful. [Urban Dictionary]
although it would be understood only by South Park fans, I guess.