If you have opportunity to enter a discussion with a JW (I am still active so for me it's not a problem) ask this line of questions.
Q) Are you going to go to the Red Cross to give blood?
A) They will answer speedily... NO! (without hesitation)
Q) Why do you feel that way?
A) They will answer that 'blood must be poured out' etc.
Q) Are you personally willing to accept fractions of others blood?
This is where the fun begins.
They have the option of a quick NO! Almost certainly they will not choose this, as they would be an immediate liar. They know that they are willing to take whatever the Governing Gods in Brooklyn dictate they can without sanction because simply put, they want to live! You can have some fun with that answer, by utilizing statements like "You'd rather die than take an immunization etc"
They have the option of saying YES! This is even more fun, as you can now express how hipocritical it is to accept blood products made from "worldly" people's blood, but be unwilling to donate. And how of course are you treating the law that "blood must bepoured out" if you are using some?
What will most likely happen is they will hesitate, unsure of how to respond. But this is the most deadly for you can then ask "Why the difference? How is it you responded so quickly to the first question, but now hesitate on this one?"
"WHAT'S THE DIFFERENCE?" is the final question that drives the nail home, right into their skull.