[Andreas]

A (maybe) easier approach:

In template phpinclude_start add

PHP Code:

$buddyarray = explode(' ', $bbuserinfo['buddylist']); 


In Template postbit
FIND

<if condition="$post['userid']">
	<tr><td class="vbmenu_option"><a href="profile.php?$session[sessionurl]do=addlist&amp;userlist=buddy&amp;u=$post[userid]"><phrase 1="$post[username]">$vbphrase[add_x_to_buddy_list]</phrase></a></td></tr>
</if>

REPLACE that with

<if condition="$post['userid'] AND $post['userid'] != $bbuserinfo['userid']">
<if condition="!in_array($post['userid'], $GLOBALS['buddyarray'])">
	<tr><td class="vbmenu_option"><a href="profile.php?$session[sessionurl]do=addlist&amp;userlist=buddy&amp;u=$post[userid]"><phrase 1="$post[username]">$vbphrase[add_x_to_buddy_list]</phrase></a></td></tr>
<else />
	<tr><td class="vbmenu_option"><a href="profile.php?$session[sessionurl]do=removelist&amp;userlist=buddy&amp;u=$post[userid]"><phrase 1="$post[username]">$vbphrase[remove_x_from_buddy_list]</phrase></a></td></tr>
</if>
</if>

And add the phrase as tmhall suggested.
The advantage over tmhalls suggestion is that this does require less processing (explode() is only executed once), and you don't have to modify the php files.