how to hide a forum from Specific gender?

[Gray Matter]

First of all, you can't use "$post" in the conditional if you're using the conditional in the "forumhome_forumbit_level1_post" template.

You should also probably avoid using <else /> by just using a negative conditional. Try this:

<if condition="$userinfo['field5'] != 'male' AND $forum[forumid] == 21">
<tbody>
	<tr align="center">
		<td class="alt1Active" colspan="2" align="$stylevar[left]" id="f$forum[forumid]">
		
		<table cellpadding="0" cellspacing="0" border="0">
		<tr>
			<td><img src="$stylevar[imgdir_statusicon]/forum_$forum[statusicon].gif" alt="" border="0" id="forum_statusicon_$forum[forumid]" /></td>
			<td><img src="$vboptions[cleargifurl]" alt="" width="9" height="1" border="0" /></td>
			<td>
			<div>
				<a href="forumdisplay.php?$session[sessionurl]f=$forum[forumid]"><strong>$forum[title]</strong></a>
				<if condition="$show['browsers']"><span class="smallfont">(<phrase 1="$forum[browsers]">$vbphrase[x_viewing]</phrase>)</span></if>
			</div>
			<if condition="$show['forumdescription']"><div class="smallfont">$forum[description]</div></if>
			<if condition="$show['forumsubscription']"><div class="smallfont"><strong><a href="subscription.php?$session[sessionurl]do=removesubscription&amp;f=$forum[forumid]" rel="nofollow">$vbphrase[unsubscribe_from_this_forum]</a></strong></div></if>
			<if condition="$show['subforums']"><div class="smallfont" style="margin-top:$stylevar[cellpadding]px"><strong>$vbphrase[subforums]</strong>: $forum[subforums]</div></if>
			</td>
		</tr>
		</table>
		
		</td>
		<td class="alt2" nowrap="nowrap">$forum[lastpostinfo]</td>
		<td class="alt1">$forum[threadcount]</td>
		<td class="alt2">$forum[replycount]</td>
		<if condition="$vboptions['showmoderatorcolumn']">
		<td class="alt1"><div class="smallfont">$forum[moderators]&nbsp;</div></td>
		</if>
	</tr>
</tbody>
<if condition="$childforumbits">
<tbody>
	$childforumbits
</tbody>
</if>
</if>