In the hopes that someone on the UY or Fanfic list can settle this:

Here to serve.
 

   I was recently in a discussion with a fan fiction writer concerning

the

nature in _Urusei Yatsura_ of the relationship of Benten and Oyuki. 

Cool.  Anonymity is prolly wise.

His
planned story falls back quite heavily (though hardly exclusively, of
course) on the bit of UY fan folklore that holds that Benten and Oyuki

are

lovers. 

<cough> Unless you make it blindingly obvious who the author is.  Mr.
Davies, could you put down the lesbians and step forward, please? ^_^

   So then: does anything in the 34 volumes of the _Urusei Yatsura_ manga
or perhaps in the UY TV series give any merit to the idea that Benten and
Oyuki are lovers, or at the very least homosexual?

The ONE manga scene that even vaguely suggests this is entirely due
to Ataru's perverted imagination.  In one of the manga (Wideban 12,
I think), Ataru gets hold of some kind of bubblegum that can create
his fantasy women (I believe; just have the original, with no
translation).  He conjures up semi-nude versions of Oyuki and
Benten and tries to hit on them; they, however, seem frightened of
him and cling to each other instead.  Lum, upon finding him, mallets
the **** out of him and loudly states that Benten and Oyuki aren't
that way.

When the anime made this, they combined it with another manga story,
and sadly this joke was cut out.  Ah, well.

So, in essence there is your answer.  About a year or so ago, I wrote a
one-paragraph jokefic that had Oyuki and Benten go to the hospital as
Benten's tongue had frozen to Oyuki's...privates.  But then, as you 
said, it's an amusing joke for ecchi fanboys...which I am. ^_^

--SG