I'm going to spoil the ending to Men In Black III.
Why would you spoil the ending to Men In Black III?
It will be fun to see my friends' reactions when I spoil the movie.
It is rude to spoil the end of the movie for someone. You would be upset if someone did this to you.
They won't be mad, I do things like this all the time.
Spoiling the end of a movie for others is a bad behavior. People look forward to finding out the ending of a movie they've watched and it's disappointing to have it spoiled. Try to think of you're friends' feelings before spoiling a movie's ending.