People with pronounced narcissistic traits exhibit marked problems in their intersubjective experiences, yet a more detailed view on how different aspects of interpersonal functioning relate to grandiose and vulnerable narcissism is lacking. We conducted a preregistered study of 956 participants to examine how vulnerable and grandiose narcissistic traits differ in relation to mentalizing, epistemic trust, belongingness, and experiences of shame. Our findings differentiated distinct inter- and intrapersonal patterns between high trait narcissistic vulnerable and grandiose individuals. Narcissistic vulnerability was linked with compromised mentalizing, increased epistemic mistrust and credulity, higher need for belonging, and heightened experiences of internal and external shame. Conversely, grandiose narcissistic traits predicted lower belongingness needs, reduced shame experiences, and higher epistemic mistrust without credulity or clear deficits in mentalizing abilities. These results highlight vulnerable trait narcissism's pronounced interpersonal instability and grandiose narcissism's defensive self-regulation and emphasize the importance of differentiating narcissistic traits to inform targeted therapeutic strategies addressing specific emotional and relational impairments.