[LifesGreatestGift]

I think he want's to use a custom user title only for his profile/posts.

You will need a conditional in your postbit(_legacy) template to replace the default user title code.
If you do not use the conditional in the below way, then everyone's user title will say I love {user browsing}!

Something like

<vb:if condition="$post[userid] == 1 AND $show['member']">
    <span class="rank">I love {vb:raw bbuserinfo.username}!</span>
<vb:else /> 
    <vb:if condition="$post['rank'] != ''">
        <span class="rank">{vb:raw post.rank}</span>
    </vb:if>
</vb:if>

Then just change the 1 to your userid

-------------------------------------
So this conditional 'says'
If this post belongs to [you] and the user browsing is NOT a guest
then show 'I love [username of user browsing]!'
else if this post isnt [you] and user title isn't NULL
display poster's user title
-------------------------------------

Not sure if this code is 100% correct, but you get the idea.