Glenda has spread false rumors about a classmate in order to ruin his reputation. Her behavior best illustrates

I believe the answer is: relational aggression

relational aggression refers to a form of agression that is being done in order to harm a person's social status. This is extremely common in all societes regardless where it's located in the world.

Most commonly, the actors of such agression choose to do so in order to increase increase their own status without actually climbing up. So, they makes other people's go down to surpass them.