Two rather insulting forms are, "As plain as the nose on your face," and (expanding on your own words), "As any fool can plainly see."
Somewhat more mystifying, and still a trifle insulting, are, "Without a doubt," or, "Requiring no explanation."
When meant in an ironical way, perhaps to avoid attempting the explanation of something that's truly complicated, you can say, "Intuitively obvious to the most casual observer." The implication is, "Even if I COULD explain it, you STILL would not understand it." It's quite handy in ending an unwanted discussion about difficult mathematics.