Establishing maladaptive personality traits at a younger age in a developmentally appropriate and clinically tangible way may alert clinicians to dysfunction earlier, and thus reduce the risk of significant impairment later in life. The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) Alternative Model for Personality Disorders (AMPD) provides a set of traits useful for organizing behavioral and experiential patterns central to daily personality functioning. The goal of the present study was to evaluate manifestations indicative of AMPD traits via ambulatory assessments in the daily lives of adolescent girls. Caregivers and girls (N = 129; age: M = 12.27, SD = 0.80) provided baseline assessments of girls' trait vulnerabilities (negative affectivity, detachment, antagonism, disinhibition, psychoticism) and girls additionally completed a 16-day ecological momentary assessment protocol (N = 5,036 observations), rating social behaviors and experiences in their daily lives. Multilevel structural equation models revealed that trait vulnerabilities were linked to more extreme shifts in interpersonal experiences and behaviors from one moment to the next, suggesting that maladaptive personality traits were linked to greater variability. Furthermore, AMPD traits were positively and strongly related to negative affect in daily interpersonal situations. More specifically, girls' trait ratings were associated with elevated mean-levels of boredom, as well as interpersonal tension. Caregiver-reports complemented this perspective of dissatisfying social interactions, suggesting that especially detachment and antagonism accounted for lower levels of social connectedness and more variability in social activities in girls' daily lives. Results are discussed in terms of the short-term dynamics and related intervention targets of developmental personality pathology. (PsycInfo Database Record (c) 2023 APA, all rights reserved).