What punctuation is this sentence missing?
There should be a hyphen between big and ass, as the two words together form an adjective, applied to mistake. (See also Ophiuroid’s comment referring to xkcd).
There should certainly be something before America; I agree with Boofus’s answer on that issue.
How it should be punctuated depends on the message. If one is telling America that it has made a big ass mistake, it should have the comma. If one is saying that America is one big ass mistake (perhaps one is British), a colon would probably be best.
One big ass mistake: America.