I think it's safe to say that here in the land of Twific, just about every line has been crossed. With all of the Darkwards, Domwards, Geekwards and Douchewards, we've stretched the definition of OOC as far as it can go and then some.
Canon pairings have proven to be just a starting point. Why stick with basic Edward x Bella when there's Jella, Roseward, and every permutation of slash imaginable?
Through it all, I know each of us has that personal line we can't cross; the pairing that feels like an unholy alliance to us, the character depiction that makes our skin crawl. So, tell me yours, campers. What can't you do? What do you see in a summary that will make you flounce before you even start?
To get us started, I'll share mine:
I can deal with small doses of almost all non-canon pairings, but never Edward x Alice. In my head, she will always be his sister. Period. I don't care if they've never even met in a particular fic. Alice x Edward is against the natural order of the universe! I just can't go there.
As for out-of-character depictions, I can wrap my brain around all kinds, but I always have a hard time seeing Charlie as a bad guy. In my head, Charlie is always soft-spoken, well-meaning, and good-hearted, and it hurts my heart a little if he's a baddie. I love Charlie hard.
And for your time, the pairing I can always read: