Psychopathy and externalizing are distinct forms of disinhibitory psychopathology whose destructive social behaviors are thought to be underpinned by different aberrations in social cognition. Facial emotion processing is a foundational component of social cognition, yet previous studies on facial emotion processing in psychopathy and externalizing have focused on traditional behavioral measures (e.g., response accuracy), which have limited reliability and precision. Diffusion modeling is a valuable tool for elucidating more reliable and precise sources of performance differences because it estimates parameters that reflect latent cognitive processes, including bias, drift rate (efficiency of evidence accumulation), threshold separation (extent of evidence accumulation), and nondecision time (time spent on non-decision-related processes such as stimulus encoding and motor response execution). In a sample of 92 incarcerated males, we applied diffusion modeling to an emotion identification task in which ambiguous blends of anger, happiness, and fear were identified while contextual threat (i.e., apparent movement of faces) was manipulated. Results indicated that psychopathy was associated with longer nondecision time (i.e., slower processing) across all the emotion blends in the task and particularly for mostly angry faces under greater ambiguity. In direct contrast, externalizing was associated with shorter nondecision time (i.e., faster processing) as well as greater threshold separation (i.e., more extensive evidence accumulation) for mostly angry faces under greater ambiguity, but this pattern of preferential processing of anger was only evident in the absence of contextual threat. These findings link psychopathy and externalizing to different profiles of cognitive processes influencing facial emotion processing. (PsycInfo Database Record (c) 2021 APA, all rights reserved).