During the Cerebus attack on the Citadel
When Udina was asked to move away from the console by the Salarian Councilor, he pushed her back. There was a renegade action, which resulted in Shepard killing Udina.
Are there any consequences of this action? What would have happened if the Councilor was let to live?
Conveniently, there's no way that he could be allowed to live. Had you not shot him, he would have been killed by Kaidan or Ashley, depending on who was alive in your game.
As a result, the only consequence is influencing the dialog with the respective character later, as they'll question you about your decision in using the Renegade interrupt.
