depends what template you want to put it in. But I would imagine something like this
OPTIONS FOR DROPDOWN
Non-Active [has an id of 0]
Active [has an id of 1]
Code:
<vb:if condition="$bbuserinfo['field#'] == 0">
<p style="margin:15px 0;padding:8px;background:#ff0000;color:#333;">Please change to active!</p>
</vb:if>
Where
# is your field id, and
0 is the id of the non-active selection.