To the editor: I enjoyed William Alexander's absurdly useful
An American friend of mine, a student in his 20s, was having an affair with a French woman in her 40s. She was socially very proper, even stern. When they were in amorous embrace, she insisted he use "tu" in their communications, but the moment that ended, she demanded he address her as "vous."
The "tu-vous" usage, in this case, was activity-driven.
Ronald Rubin, Topanga