It's a double standard.

Meaning

Different rules are applied to different people.

Examples

• John: He got away with it but I got punished.
• Alice: That's not fair. <b>It's a double standard</b>.
• John: Exactly, and it's infuriating.
• Alice: It's truly unfair. Applying different rules based on favouritism is unacceptable – <b>it's a double standard</b>.