Here is a talking point that may resonate with some old-timer JWs, especially those who recall the often vitriolic pronouncements against Catholicism in the 60's & 70's, and even thru part of the 80's....
One of the points I recall that was looked on with scorn and derision by many JWs was the idea of "papal infallibility". "Look at those pagan Catholics,", a particularly rabid JW might comment. "They think their pope is perfect--they even have a doctrine called 'papal infallibility!!"
"Papal infallibility", however, is one of the more misunderstood Catholic doctrines. Here is what Wikipedia has to say:
In Roman Catholic theology, Papal infallibility is the dogma that the Pope is preserved from error when he solemnly promulgates, or declares, to the Church a decision on faith or morals.
I.e., the "infallibilty" part only applies to proclamations of doctrine, and only in certain specific occasions. Catholics absolutely do not believe the Pope is "perfect", or that he "cannot lie".
If you can get into a dialog with a JW, and have a chance to point this out to them, you can next mention, "Of course, JWs have an equivalent doctrine in tehir religious system."
This will undoubtedly and immediately be met with scorn and derision.
Upon which you reply, "Well, what about proclamations given by the 'Slave' in the pages of the Watchtower? You of course admit that the organization is made up of 'imperfect men', but do all JWs believe that the words provided by the 'Slave' are absolutely true? Or can you be a good JW and have numerous, or even one, opinion, different than the 'current understanding' of matters?"
This alone may be enough to cause a mental hiccup. Others may reply, "But there is a difference. The Pope's proclamations often conflict with [the JW understanding of] scripture. Everything the 'Slave' says can be backed up by one or more scriptures, and the citations are always given in the Watchtower."
At which point you reply, "Oh?? Tell me, which scriptures support [insert your favorite non-scriptural JW doctrine here]?"
A few ideas which pop into my mind are:
-- Which scripture is it that says that if a person accepts a transfusion of 'fraction X' from blood, he must be disfellowshipped, but if he conscientiously accepts 'fraction Y', everything is perfectly fine?
-- Which scripture is it that talks about private reproof, public reproof, imposition of restrictions upon repentant sinners, etc.?
-- Which scripture is it that states that elders (or any male, essentially) cannot have a beard?
-- Which scripture definitively determines that the 'faithful and discreet slave' of Matthew 24 is the same as the '144,000' or Revelation 7?
and so on.
Anyways, I couldn't sleep last night, and this is the idea that popped into my mind.