Facial expressions are important in social interactions, where they are often mutually exchanged in face-to-face situations but little is known about the factors that influence such deliberate expressions. Here, we investigated the effect of personality characteristics on voluntary facial expressions. A short statement describing a positive, negative, or neutral characteristic of a target person was followed by her smiling or frowning portrait. Participants were to imitate this expression. Reaction times and accuracy of the facial responses were derived from electromyography of M. corrugator and M. zygomaticus major; in addition, EEG-derived event-related potentials (ERP) were obtained. Responses were faster and more accurate when facial expressions were congruent with the personal characteristics. Congruency effects in ERPs, were observed in the P200 component, the early posterior negativity (EPN), and the P300. Hence, personal characteristics can modulate the deliberate imitation of facial expressions, based on modulations of reflexive attention and proceeding through several cognitive processing levels. This is the first demonstration that deliberate expressions of emotions are influenced by affective knowledge about the communication partner.