Jeff looks at her and acknowledges something special is happening; by the end of the night he's climbing the stairs to the fifth-floor walkup Karen shares with roommates.
Once inside Karen's room, Jeff grabs his phone and taps a few times.
Karen's phone beeps with an incoming text. She's received a WhatsApp message: "Jeff is requesting sexual consent." There's a heart-shaped icon for yes and an X for no.
Karen can tap the heart and appreciate the fact that Jeff cares about consent. Or she can tap the X and wonder what kind of guy has a sex app on his phone.
This hypothetical situation isn't some future shock "Black Mirror" fiction. A Dutch blockchain company is developing an app called LegalFling that creates sex contracts between consenting adults.