Alternatively, perhaps they do have a stake in the outcome and are confident that somebody they don't like is about to receive a well-deserved comeuppance, or that their side is winning in the case of a fight, or that their Evil Plan is about to come to fruition if it's a villain doing it.

It may also indicate that the character in question has no stake in the outcome. This is always used for humor it often indicates that the character in question, rather than offering to help, is callous enough that they are deriving amusement from someone's anguish or anger. Almost inevitably, the character will be too fixated on the entertainment to actually look at what they’re eating. Usually, the scene will be something like a fight or a private conversation between lovers, that generally isn't intended for anyone's amusement (at least not in-universe).

When a character is treating a certain scene as pure entertainment, they will often be shown eating popcorn or other stereotypical movie-theater food.