Shia LaBeouf -- Insane Patriotism At Mt. Rushmore (VIDEO)

Shia LaBeouf displayed raging patriotism over the weekend at Mount Rushmore.

Shia's fellow tourists tell us, they thought they he was just a random crazy until they got close ... then realized the guy without the shirt was the famous actor, screaming "AMERICA!!!!!!"

An old lady eventually asked LaBeouf to tone it down ... and things got weirder. We're told LaBeouf claimed he was a Marine and then asked her on a date.

Shia's in the area filming "American Honey," where he suffered a gnarly head wound last week during an accident on the set.