LOL. I think I saw this before. Pretty hilarious.
Add to that the hair difference, the glasses (I got new lenses a couple of years ago and when I don't wear my reading specs my kids think I look weird), the posture, the attitude, the soft layered clothing Clark wears as opposed to the skin-tight Superman suit, and it's no wonder that people who have only a passing acquaintance with either Clark or Superman don't connect them.