Back in the early sixties, it depended how well you knew someone. A first dinner date, you tried to make sure that you excused yourself before the meal, and if necessary afterwards. Most young men would tactfully know perfectly well that you were off to the loo, as you did with them. Once you knew someone better you just said ' need the ladies' or whatever! I never found it to be an issue, but I wouldn't have said bathroom as that indicated having a bath!!!! Maybe cloakroom in the early days?!