It started for me with reading "Jehovah's Witnesses in the Divine Purpose." It's a sort of JW Apologia. I thought it was absurd how the JWs applied to themselves all sorts of prophecies and how they made the most incredible connections. Like claiming their little pamphlets they handed out prior to an assembly in Pittsburg, I think it was, were like "tongues of fire falling from heaven on the heads of non-believers" spoken of in the scriptures.
And applying to the guys who went to jail for refusing to serve in the military in WWII the prophecy about the "two witnesses" who were dead, then not dead, then dead again, only to be resurrected and I disremember what else.
They also had explanations for certain selected, but not all, of the nutty things that went on with Rutherford and some young chick, and Beth Sarim, and miracle wheat, and on and on and on and on. I thought, "this is the weakest argumentation I've ever heard in my life. And some of the things that happened in the past. My God, what a buncha bozos. And this represents GOD?"
Strange as it may seem, it was the beard issue that was the proverbial straw. And the three guys they sent over to "adjust my thinking" on that matter. One stole electricity with a power meter when he cleaned apartments, one was a noted boozer who was shit-faced when he got to my house, and the last was also a petty thief. Essentially, I kicked them out.
So it was their own book, coupled with the beard issue that did it for me.
Francois