I like what GoY pointed out:
I'm very much pro-letting the admins do the titles. I think it really adds to the community, and is especially helpful in giving newer members a chance to kind of...get a feel for the place, I guess...get a good, humorous first impression of everyone before they dive into posting. Okay, I may not be able to make a great case for it, I just like the idea.
However...if such a system were put in place, you don't want people to assume that it's the admins job to supply custom titles, or else everyone would be complaining until they got one (kind of like everyone was before we all got a title...)
So it'd be tricky. Of course, you could always try and enforce a "don't ask about custom titles" rule, if you wanted. You could have a sticky, sort of "post here if you want a custom title thread," but you'd probably get a majority of new members who haven't really added anything to the community yet going to that thread first, and then being disappointed their title doesn't reflect all the facets of their personality. (Not to mention that a thread like that would probably keep the admins way more busy than they'd like.)
So letting everyone make their own titles is definetly the easiest way to go. But if there was a sensible and effective way of letting the admins handle the titles, even (or especially) if it meant not everyone getting one right away, then I'd be all for it.
...Yes...that's what I think.