Discrimination is when you treat a group or its members negatively for unjust reasons.
Please note that this video may be seen as offensive. It says the A word once, and the GD word once. Plus it makes fun of redheads.
Cartman, and many of his fellow students, display hatred towards redheads. The town doctor even expresses his belief that redheads should be put down because they have gingervitus. This hatred does not have a just cause but is rather based on the belief that redheads have no souls. This is clearly an example of discrimination. The redheads in South Park are treated badly only because of false beliefs the students and town members hold.