Sentence-final particles (SFPs) as bound morphemes in Japanese have no obvious effect on the truth conditions of a sentence. However, they encompass a diverse range of usages, from typical to atypical, according to the context and the interpersonal relationships in the specific situation. The most frequent particle,-ne, is typically used after addressee-oriented propositions for information sharing, while another frequent particle,-yo, is typically used after addresser-oriented propositions to elicit a sense of strength. This study sheds light on individual differences among native speakers in flexibly understanding such linguistic markers based on their mentalizing ability (i.e., the ability to infer the mental states of others). Two experiments employing electroencephalography (EEG) consistently showed enhanced early posterior negativities (EPN) for atypical SFP usage compared to typical usage, especially when understanding-ne compared to -yo, in both an SFP appropriateness judgment task and a content comprehension task. Importantly, the amplitude of the EPN for atypical usages of-ne was significantly higher in participants with lower mentalizing ability than in those with a higher mentalizing ability. This effect plausibly reflects low-ability mentalizers' stronger sense of strangeness toward atypical-ne usage. While high-ability mentalizers may aptly perceive others' attitudes via their various usages of-ne, low-ability mentalizers seem to adopt a more stereotypical understanding. These results attest to the greater degree of difficulty low-ability mentalizers have in establishing a smooth regulation of interpersonal distance during social encounters.