Yeah, the vb:comment tags aren't working like I thought the should - I don't know why. But the problem is the first vb:if tag you're trying to comment out isn't getting commented out, and there's no corresponding </vb:if>. I guess if you really want to keep it in there you'll need a closing tag, like:
Code:
<vb:if condition="$show['avatar']"></vb:if>
Yes, you can use html comments in a template, but they just get passed through to the browser. They don't affect the template compiler, so they don't work to comment out the special template tags.