When I was in college, my then girlfriend texted me that she was watching Jojo Rabbit. She knew it was one of my favorite movies, and said that she loved it too. She was talking about how Scarlett Johannson's shoes almost have their own personality. So I said,
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yeah, it's devastating when you notice her shoes on the hanging body.
Turns out she had paused the movie to make some dinner, and hadn't seen this part yet. Needless to say, she was PISSED!
Not me personally, but when I was hanging with a couple of friends we talked movies with good twists and of course classic The Sixth Sense came up. One of my friends says he hasn't seen it, yet. So of course we recommend it to him and don't say anything about the twist. Unfortunately another friend was just coming back from the toilet and hadn't heard that someone hasn't seen the movie, yet. Only heard us praising the Sixth Sense, so comes back and directly goes:
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Oh yeah! Bruce Willis is dead the whole movie! What a twist!
I saw this with some friends, about 5 minutes in my friend leaned over and was like 'so he's a ghost too and he doesn't realise?' and I was like "Ohh, I hadn't realised that yet". We watched the rest of the film thinking how sad it was that his wife didn't know he was there, then at the end and that was revealed it was super confusing.