Dean and Sam ('Supernatural')
Just a big giant "eww" on this one, you guys, because Sam and Dean are brothers, as in they share the exact same parents, as in they are related by blood. Which of course doesn't matter to the legions of slash-fiction writers out there who take it upon themselves to regularly pen stories about Sam and Dean's sexual/romantic exploits (in case you were wondering, Sam is generally the top and Dean is generally the bottom). According to supernaturalwiki.com, common themes in such stories include but are not limited to "We couldn't help ourselves," "Incest taboo," and "And then they had sex," which I would just like to point out are all literally the same exact theme.
- Chris Eggertsen