Well, no kidding, if you're literally going up and saying /that/, which doesn't help anything but your ego IMHO.
Learn to deliver criticism properly! How about "I think the icon is misleading: I saw customer X interpret it as ..." or "I think the icon doesn't fit the style of the rest of the thing, look at how all the other ones are using pastel colors and this one ..." or "The icon is too low-res and looks pixelated on my monitor" etc? The point isn't that they are wrong and you are right, it's that it could / should be better in a certain way.
Also, go in with some dignity and not with the assumption that the person is incompetent: perhaps they had some other goal or an absurd deadline or a constraint that they were working around and not "you missed this obvious thing that even I could see, doofus".
Also, first tell the person privately and casually, in an environment where they don't feel pressured to maintain appearances: like it or not, there is a stigma around making mistakes in most offices (or learned behavior on some people's part) that doesn't work to anyone's advantage. So don't blurt out "the icon is wrong" out of nowhere in the middle of a meeting with superiors or "ha ha, GEEEZ DID YOU MESS THIS ONE UP" in the middle of the open office.
Sure, if you've been tactful and helpful and still being ignored and it's important, then raise the issue above the person. But gosh, being tactful is a learnable skill.
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Edit: I think the quality of the interaction mostly really comes down to: does the person think you're genuinely trying to be helpful or that you're just trying to point out that they're wrong (and perhaps get brownie points yourself)?