a blind man could see this/that/it

a blind man could see this/that/it

This/that/it is very clear, obvious or apparent. Emily has a crush on Josh? Yeah, no kidding, a blind man could see that. A: "He's having a hard time hiding his stage fright." B: "Um, yeah, a blind man could see it."
See also: blind, could, man, see, that, this