Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

Two zombies are sitting together eating human victims. One zombie is eating a male victim, and the other zombie calls him out: "You're eating dudes? GAYYYY." The caption below reads: "I'm beginning to regret zombifying that frat boy."

The joke works on two levels. First, it applies the absurd homophobic logic of stereotypical "bro culture" to the context of zombie cannibalism -- a frat boy zombie somehow finds a way to make eating brains into a question of sexual orientation, based solely on the gender of the victim. Second, it satirizes how the hypermasculine policing of behavior found in certain social circles can persist even in the most extreme and irrelevant circumstances. The other zombie's exasperated caption suggests that the frat boy's obnoxious social attitudes have survived the transition to undeath entirely intact, making him an annoying companion even among the living dead.