The research considers attitudes toward personality traits in online social network (OSN) Vkontakte users’ behaviour. Users’ friends’ activity on a given user’s profile was supposed to be affected by attitudes toward traits of the latter. Within a broader context, the role of metacognitive type of characteristic adaptations as a key element of the five-factor theory of personality is studied. Accordingly, along with attitudes toward traits, other metacognitive characteristic adaptations are examined (e.g. dispositional efficiency, reflected trait, and reflected attitude toward a trait). 1030 undergraduates participated in the study. The research results confirm that extraversion is the most important predictor of OSN behavior among other personality traits. The information presented in this research is obtained using behavioural data instead of more convenient self-reports. Moreover, these behavioural data characterise other users’ (friends’) behaviour while addressing a certain user’s profile. Positive attitudes toward each Big Five traits (extraversion, agreeableness, conscientiousness, emotional stability, and openness to experience) separately affected the number of “Likes” of the avatars representing users’ photographs. Furthermore, revealed correlations between traits and “Likes” were subsequently eliminated by the attitudes toward respective traits. Positive attitudes toward conscientiousness predicted the increase of friends’ number unlike trait conscientiousness. Positive attitude toward agreeableness predicted the increase of the number of posts written by friends on user’s wall unlike trait agreeableness. Attitudes toward traits are argued to affect social environment governed by an individual: one may select those social relationships and partners that fit better one’s attitudes toward traits. This, in turn, may affect actions of other people towards the given individual including those of online behaviour.