Do you guys periodically do reality checks while watching a movie or reading a book or playing videogames?
Do you think that ruins the experience?
No, but it would be an interesting idea, especially with games. I don’t watch much TV, and I can’t remember any dreams about books, but game dreams are frequent for me.
Reading books uses our visualisation ability, so it would in theory make sense to link that with lucid dreaming…
If you have to focus on remembering to RC it does affect the experience. I would rather just focus on immersing myself in the game/movie/book and later tell myself that if I see stuff from it in a dream, I’ll realize it’s a dream. Visualizing the scene would be good too.
From my opinion this way would be the best to be sure that you are or aren’t in a dream because that’s the point of RC’s to stop the current actions that you are doing and focusing on the idea of being in a dream. Does it ruin the experience? I would say yes but it’s not that you can’t pause the game or a movie nowadays or stop reading book for this few seconds/minutes and if you are in cinema then just a quick RC won’t actually ruin your experience it just might enhance it! 
When I play games, especially games like Minecraft, I occasionally try to pretend like I’m in the world and that there’s the chance I could be dreaming in that world. So I’m walking around in the dark or something, for example, and I do a double-take cause of something I saw; I’d generally do a reality check or tell myself it could be because it’s a dream. Sometimes I treat the game itself as if it were a dream.
I don’t think it ruins the experience at all… I just find it hard to remember that I could be dreaming when I do something that requires a good bit of my focus. 