When two individuals sitting adjacently engage in separate but complementary go/no-go tasks, with each responding to only one of two non-spatial attribute (e.g., color; one to red and the other to green) of a stimulus presented on right or left sides, responses are faster when the actor and the stimulus are on the same side. The present study investigated the role of task complementarity in this social Simon effect by assigning same (e.g., red/green) or different (e.g., red/square) target feature dimensions (color/shape) to the two participants. We also investigated the role of response complementarity by manipulating the proportion of trials to which both, one, or neither of the participants responded. A comparable social Simon effect was obtained irrespective of target or response complementarity. We conclude that what is represented in the social Simon effect is the action, rather than the task, of the adjacent partner.