Commander William Riker, the most sexually promiscuous Enterprise (and perhaps Starfleet) officer, is, perhaps appropriately, the one most concerned with consent in sexual activities.
This was crystallized in the episode "The Vengeance Factor" (S3E09) when Riker was unable to engage in sexual congress with Yuta, servant of the Acamarian Sovereign, who is not free to make her own choices. Because she is behaving subserviently, he cannot ethically proceed with a physical relationship. As he tellingly remarks, "I prefer equals." And he means it.
It was also challenged in the episode "A Matter of Perspective" (S3E14) when the wife of scientist David Krieger accuses Riker of unwanted advances. Troi impossibly suggests that both versions of the story are true to the opposite sides of the trial, but we all know that Riker is all about enthusiastic consent.