Why does Beauchamp steal Mary Ann's scarf in the novel, Tales of the City?

During his weekend affair with Mary Ann, Beauchamp steals her scarf and then hides it in the car for DeDe to find. Why he does this is never made entirely clear; perhaps he's simply trying to upset his wife as he's that sort of guy. In any case, the scarf is a catalyst for the deepening deterioration of Beauchamp and DeDe's marriage and, in a strange way, also a catalyst for a mutual respect between DeDe and Mary Ann that, later in the series of books, develops into a powerful alliance and a strong friendship.