Prick a Lannister, does he not bleed? Tickle a Lannister, does he not laugh? Catch a Lannister having sex with his sister, will your 10-year-old son not be thrown off a tower? Much as we like blond-on-blond lust—especially where walking eye-candy Headey and Coster-Waldau are concerned—their murderous issue, King Joffrey, is the final, definitive answer to why incest is very, very wrong.