Fan Casting Kick the Dog in Sort by Tropes

When a character does something evil, cruel or very mean for no apparent gain, because the author wants to demonstrate that they are not a nice person and shift audience sympathy away from them. What separates this trope from a character's other evil or cruel acts is that this bit of evil is gratuitous. It doesn't get the character anything or even advance the plot. The sole reason for this story beat existing is to place one or more characters squarely on the wrong side of the Rule of Empathy.