I play this game with people who claim to believe in God where they believe in God having omniscience, i.e. foreknowledge of everything.  I point out to people you can't have free will in such a circumstance.  They don't like it so I'll offer to play a game with them.

One of the points of this is that the whole thing is intended to be for fun, I just want to stretch their mind a little and give them something to think about.  I'm not trying to change their opinions nor do I expect to convert them to something else.  I find it fun because I can practically guess most of their responses and it's fun to watch them try to struggle to get around the contradictions in their thinking. 

So, anyway I'll point out that you can argue - as in make a case for something, not as in have a fight - that there is an omniscient God who knows everything, or you can have free will and the ability to make choices of your own.  Either is reasonable to argue, but you cannot argue both simultaneously because they contradict each other.

I give an example, say that God knows everything about you, from before you were born, until after you die, and knows every possible choice you will make on every decision.  Given this to the the case, it is clearly impossible for you to have free will, since all of your choices are known in advance. 

They'll usually offer some weak argument about how you don't know the choices and thus you have free will.  I point out that if you're watching a movie, the movie can't decide to change the script and the events that are shown in the film are frozen and thus cannot be altered.

What I have found - and this is what makes it fun - is that it is practically 'predestination' on the part of a religious person, sooner or later, as part of the discussion, they will point out that God never made anyone do anything.  I'll then point out I never said that was the case.  If I want to shock them a bit, I say something like, "I never said She did."  

I've met a few people who readily agreed you can't have free will and omniscience, some who admitted it was obvious.  I met one very smart lady, who, despite being Catholic, also agreed that you can't have an omniscient God and free will together.

The reason this concept bothers people is because if God is omniscient, then by definition you cannot hold people responsible for their actions, any more than we can blame a runaway car for the damage it causes.  But carrying both the concept of an omniscient God and being able to hold people responsible for the decisions that they had no capacity to make free choices is a concept a lot of religious people like to have.  It's on the level of the class of people that think that it's wonderful that sinners go to hell and are tortured forever, while they've got it great in heaven because they have some special 'in' with God.