I haven't had reviews on my stories that are too crazy (I think I've left some pretty loopy ones on other's stories...), but the following fairly récent review I received from a certain lovely 'akatsuki fan KYAAAA' made me laugh: "i command toi not to be busy and finish this wonderful story, ou i shall hunt toi down and force toi to...have a nice day"
I write M rated stuff. It shows in the story ratings. I warn my readers in my author's notes.
One day, I had a review after a rather steamy scene involving a blowjob and the reviewer wrote to me that this was utterly disgusting !
It amused me to no end as I don't think that blowjobs are that dirty (honestly). I replied to them that the story was M rated, that they had been warned and after several chapters of "adult" situations (whether sex ou violence), I expected my readers to montrer an equally "adult" reaction.
I usually bet on people's intelligence and maturity. But it happens I'm sometimes wrong.
I got another one, funny this time, about a HP fanfic pairing Severus with an OFC, but without Harry, Ron & Hermione. A reader wrote me a lovely review, after something like 50 chapters (there are 138 chapters in that story), stating that they had just realized there was no Harry at all ! It amused me a lot too and I kindly replied to them that I had specified this in my notes. The review was positive but the way the reader wrote their review was fun to read.