We investigated the processing of faces with different smile expressions according to a context of personal performance. Individual judgments of smile happiness were collected to assess the processing of different types of smile when these were presented as a social response in a cognitive conflict task. Two main factors were considered: (a) Expression characteristics of the smile were manipulated: that is, happy (happy-happy), neutral (neutral-happy), or sad (sad-happy) eyes were morphed in faces with smiling mouth; (b) The performance context in which the smiling face appeared as social response (after fast, average, or slow correct response). Participants rated happy-happy faces the happiest followed by neutral-happy faces, then sad-happy faces (happy-happy > neutral-happy > sad-happy). Moreover, faces were rated more happy after fast responses as compared with average or slow responses (fast > average > slow). In addition to subjective ratings, we recorded the electroencephalography (EEG) and calculated event-related brain potentials (ERPs). The ERPs showed modulations of early visual potentials according to the expression characteristics of the face. The P1 was larger for sad-happy than neutral-happy faces. Moreover, the relationship between performance and face had a significant impact on the early posterior negativity (EPN), an ERP component associated with emotion processing. Faces elicited the largest EPN amplitude after average and slow responses as compared with fast responses. These results show that smile processing and interpretation are determined both by the distinctive perceptual features of the smile expression and by the performance context in which the smiling face occurs.