Having not seen the avatar, I can't really comment on this particular case. But, in principal, this leaves a bad taste in my mouth. Now I'm not for all out porn on the site(or any really). But it seems pretty mild when you think(as far as I know) there isn't a single starwars anything, without killing.
It just strikes me as odd that I can spend all day lopping heads and arms off anakin skywalker, but once I come on the forum and see a 70x70 gif showing, oh my god, breast! That this should offend me? Forgive me but I'm a little unimpressed. True I would look at the user that had that as their avatar as a little suspect, maybe a little juvenile, but I think that's a good thing. I know without interacting with that person that we don't see eye to eye on at least one issue.