Looks like this Yahoo! Style writer was trying to be excruciatingly correct, but wound up being completely wrong:
The word she should have used is whoever, because it’s the subject of the verb wears.
If you’re unsure if you should use who or whom (or whoever or whomever), go with who (or whoever). You’ve got a 50-50 chance of being correct. If you use whom or whomever and you’re wrong, you look like a pretentious high school dropout.