When has a spoiler helped ruin something for you?

The new Star Wars film was released 2 days ago, yet I was unable to see the movie without first having plot complications sprung on me by people who thought it was cooler to show that they are in the know, than let you experience the story cold.
If we can keep specifics of the new Star Wars movie OUT of this discussion for a couple weeks, I am sure many will appreciate it.
What else could compel someone to ruin other people’s experiences with information?