Self–other agreement (SOA) discrepancies are commonly interpreted as a lack of self-awareness. The consistent display of such discrepancies could be considered a behavioral manifestation of biased self-perception. In extreme forms, we propose that this bias can be viewed as a form of dark personality. Using archival data from a multisource instrument, we examine the derailment implications of self-enhancement (i.e. overrating) and the opposite tendency, self-diminishment (i.e. underrating), in collectivistic (Taiwan, China, South Korea) and individualistic (United States of America) cultures. In particular, we examine whether individuals whose biased self-perception tendencies violate cultural norms are perceived as more likely to derail. In both culture types, individuals with small SOA discrepancies and high ratings on managerial competence were perceived as less likely to derail. However, the implications of self-enhancement and self-diminishment were culturally contingent. Self-enhancement was not related to derailment in individualistic cultures, but in collectivistic cultures, which endorse the norm of modesty, individuals who overrate (self-enhance) are perceived by their boss as more likely to derail. Substantial underrating (self-diminishment) was also related to higher perceived likelihood of derailment in collectivistic cultures, but in individualistic cultures, some evidence suggests that self-diminishment may be related to decreased perceptions of derailment.