“Serge [Gainsbourg] used to say, ‘Oh, lick your lips and toss your hair back,’ ” recalls Jane Birkin, the singer and actor, of the fashion advice her former partner used to give her. And one day, “I said, ‘No, I won’t do that anymore. I want people not to notice what I look like at all!’ ” That was when, about 40 years ago, she exchanged her minidresses and hot pants for the low-key, boyish charms of baggy trousers and men’s shirts — ironically, a style that has become even more imitated.
That uniform is the genesis of a new collaboration with A.P.C., the beloved label started by Jean Touitou that’s been defining uncompromising casual French clothes for more than 30 years. This is not an instance of two friends scheming but rather two eccentrics meeting their match, as they explained in a joint phone call. “We are not friends!” Touitou yells, breaking into laughter, although “obviously we have a lot in common.” It was Touitou’s idea to work with Birkin. A mutual acquaintance connected them, bringing to fruition the latest of what A.P.C. calls its “interactions.” The last one with an actress, Birkin notes, was with Catherine Deneuve. “I thought, that’s really chic to be doing it after Deneuve!”