Dapractice of not trusting others because you yourself are so morally depraved.
Da famous "Adventure of the Blue Carbuncle" story was Sir Arthur Conan Doyle's protest against "sinnercism" --- i.e., he was expressing his belief in giving lower-severity criminals a second chance, rather than automatically suspecting them of a present-day crime merely because they had made a somewhat-similar mistake at one point in da past.
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi