Happens loads and loads of times in Fan Fiction, where, because Most Fanfic Writers Are Girls, the usual genders are most frequently seen flipped, with the female getting double-teamed by the two hot male characters the fic writer can't choose between.
Dear TV Tropes: consider that OT3s are sometimes not a matter of "can't choose", but rather CHOOSES BOTH.
No love,
Guardian's Song
(And yaaaaaay, totally handwaving every fic where it's two OR MORE girls and a guy! I totally imagined all those Harem Fics on FF.net, guys!)

My apologies, but I've shifted over the years from automatically mocking the "fanbrats" to regarding the more "enlightened" fans with as much suspicion as their simpler counterparts. There's an awful damn lot of talking down to female fans when male fans are let off with a smile and a wink, for one.
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I also note sullenly that the Rooting For The Empire page looks an awful lot like the Draco In Leather Pants page from the other side of the strawman. Take that as you will.
Though it does have at least one wonderful quote.
"[...] Twilight features the three tracker vampires who are trying to kill Bella, which is seen by some as a sympathetic aim. "

And this linked page (http://flyingmoose.org/tolksarc/theories/arag_arw.htm) has one very amusing quote:
"How would you react if the descendent of Charlemagne showed up in Paris today to claim kingship over France, bringing in the shroud of Turin as the evidence?"

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TL;DR - TV Tropes is at its best when people aren't opining on things, since it's not exactly objective, despite all pretenses. Fortunately, I was mainly on TV Tropes to read through the Yandere page... :D Wish there were more examples of two-way yanderes, but I suppose one has to do that oneself.

( Discussion of Bella and Edward, Fail!Yanderes (and briefly Alice, a not-so-fail!yandere...) )