Eyeholes are strange cereals that appear in the episode Interdimensional Cable 2: Tempting Fate. When someone is caught owning or eating Eyeholes, the Eyehole Man comes to him and starts beating him up.
Rick and Morty are watching interdimensional TV when they see a Eyeholes commercial. In this commercial, two aliens are kissing each other with their eyeholes on their faces. But then the Eyehole Man comes in their house and starts yelling that he is the only one allowed to have Eyeholes and removes their Eyeholes from their faces.
In the post-credits scene, Jerry finds a Eyeholes' box in Rick's cupboard and gets attacked by the Eyehole Man.