Eugene Volokh noticed a shirt that says </hate>, which presumably means “end hate”. Eugene points out that what it’s really saying is “end hate for now” and will probably resume later, since most </i> are on documents that resume italics later (or at least reserve the right to).
I bet the guy has a <hate> T-shirt in his closet that he was wearing three days before; he’s hated all the stuff between then and the </hate> shirt; and he’ll be wearing the <hate> shirt next time he’s got some hating to do. Plus he certainly wouldn’t just wear the shirt without having worn <hate> before, and on the same page — that would be syntactically non-compliant.
So the solution would then be a shirt that says </hate></html>… except that might just call for the end of mankind, which would kind of defeat the purpose.
I found this by way of Dustbury, who points out that <i> is, in fact, being retired (or at least depricated) in favor of <em> by the powers that be.