Oh, I've seen plenty of nasty assessments made of Buffy/Angel and Buffy/Spike - usually from each other's shippers. ;) But then, neither of those couples ended up being Eternally Ever After With Supernaturally-Speedy-Growing Spawn like Bella/Edward. I think another thing that helps B/A and B/S in the mocking department is that at least with them the melodrama was punctuated by moments of wry self-mocking, whereas I get the impression that doesn't really occur with E/B: it's always Big Serious Twu Wub. I've never seen True Blood so I can't speculate at all there.

A/P gets labeled creepy because the mutual obsession is right out in the open for everyone to interpret, whereas the non-canon ships you can write as being creepy or non-creepy as you want. Although I've yet to see a non-crackfic scenario where, say, Anakin/Ahsoka is not at least somewhat creepy. (Fixating on a slightly older woman who clearly wants him his creepy, yet lusting for his jailbait, hero-worshipping pupil is not? Okay.)