Someone who's rude, lazy, useless and most importantly, disgustingly dirty
This can also be used to imply poor quality in regular objects. For example: Dil-mobile (Shit box), (garbage car)
That guys is such a Diljoy.
That's a dil-mobile Dilly-office
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