This study explores the associations among narcissistic traits, interpersonal behaviors, and aggression using repeated, situation-based measurement. We examine narcissism's relations with aggression across three levels of its theorized hierarchy (level 1: narcissism; level 2: grandiose vs. vulnerable narcissism; level 3: antagonism, agentic extraversion, and narcissistic neuroticism). Using an experience-sampling approach, the current study examined the effects of narcissism and its finer-grained components on daily affective experiences and aggressive behaviors in the context of interpersonal interactions. Data were collected from 477 undergraduate students who were instructed to complete four prompts a day for ten consecutive days. Narcissism at the global construct level positively predicted multiple indices of episodic aggression (i.e., aggressive temper, aggressive urge, verbal aggression). At the dual-dimension level, grandiose narcissism specifically predicted aggression, and then at the trifurcated level, interpersonal antagonism predicted aggression by itself and in interaction with event-level negative affect. Negative affect consistently exhibited both within- and between-person effects on aggression. In real-life social interactions, narcissism dimensions differentially affect the way individuals experience social interactions and process negative affect, and thus in both research and clinical practice, narcissism is best assessed as a heterogeneous, multidimensional construct.