Social rejection can increase aggression, especially among people high in rejection sensitivity. Rejection impairs self-control, and deficits in self-control often result in aggression. A dose of glucose can counteract the effect of situational factors that undermine self-control. But no research has integrated these literatures to understand why rejection increases aggression, and how to reduce it. Using the I(3) model of aggression, we proposed that aggression would be highest under conditions of high instigation (rejection), high impellance (high rejection sensitivity), and low inhibition (drinking a beverage sweetened with a sugar substitute instead of glucose). As predicted, aggression was highest among participants who experienced social rejection, were high in rejection sensitivity, and drank a placebo beverage. A dose of glucose reduced aggression, especially among rejected people high in rejection sensitivity. These findings point to the importance of self-control in understanding why social rejection increases aggression, and how to prevent it.