It's rude to laugh during a serious movie.
Keith is at the movies watching a movie where a man just died.
Keith wants to express himself at the scene in the movie.
Keith starts to cry silently from his seat in the theater.
Keith starts to laugh loudly at the scene in the movie.
Another person in the theater gives Keith a tissue to wipe his eyes.
The other people in the theater are annoyed and tell Keith to shut up.