[toonysnn]

<vb:if condition="$post['userid'] > 0">
<img src="{vb:raw post.avatarurl}" alt="{vb:rawphrase xs_avatar, <vb:if condition="$post['field16']"><span style="color:red;">[{vb:raw post.field16}] </span></vb:if>{vb:raw post.username}}" />
</vb:if>

That should work fine .. I can't test it at the moment, but it should work without issue.

I haven't read entirely what you want to accomplish, but going off of Mikey's comments and what I see slightly in the first post...