I am almost infinitely persuadable when it comes to pairings, provided they involve one or more characters I care about, so this question almost doesn't compute at all for me.
I have a distinct memory of this WRT to reading fic: not long after I got into Buffy fandom it occurred to me that someone, somewhere, must be writing Giles/Buffy. Age differences and power dynamics and Giles are all relevant to my interests--surely this would make for kinkywrongfun reading experiences!
Yeah, I have never been squicked harder in my life except for that one time I tried to read Steve Yzerman slash and my eyes actually filled with tears to spare me the sight.
I did do something kind of similar once--similar to my Giles/Buffy experience, not, thankfully, similar to ill-fated excursions into NHL RPS--in my own writing. I tried to write Don Eppes/Colby Granger. Powerplay, age difference, secrecy but not as much secrecy as Don/Charlie! In principle, I find this pairing intriguing! In practice, I wrote something like ten thousand words of fic which kept falling further into some hideous and incoherent rabbit hole, located an ending of sorts, sent it off to beta, revised, sent it off again, attempted to revise, realized that these problems were in fact really, really fundamental and also I was starting to hate the fic a lot, and finally declared defeat and went home. I think it's the only fic I've ever written to something like completion and then stuffed into a drawer; certainly it's the longest. I simply could not make the fascinating dynamic that worked in my head work on paper. Among other things, there was no way to make a roughly canonical Colby that crazy without doing a lot of setup I didn't want to do. (I was, at the time, about halfway through doing all the setup in the world to make Don and Charlie crazy enough for each other. I did not need another crazyfication epic.)
I eventually did succeed in writing Don/Colby a couple of times after that, by the expedients of not actually exploring the relationship dynamics at all and sticking to drabble length. So possibly Don/Colby doesn't count, but that one awful story is my one big failure to write a pairing I set out to write--getting distracted by something shiny and wandering off before I finished that Clone!Ten/Rose epic, or the Bones love triangle with Sully, hardly counts.
As for writing a pairing I didn't like but found I could write anyway, uh, hm. As I said, I'm vastly persuadable, so by the time I've worked my way around to writing, like, The Doctor's daughter and a Dalek, I'm convinced that they're MFEO anyway. I guess Red John/Patrick Jane was probably the most self-consciously sincerely wrong pairing I've ever successfully written.
(The most self-consciously wrong pairing that I was never able to write--both because I was forbidden by everyone I told about the bunny and because I myself couldn't really bear to have it in my head enough to properly write it--was Gerard and Mikey Way, bodyswapped into each other. For whatever that's worth.)
( All 30 questions, under the cut. )