As an aged stickler, I'm afraid I never accept very bad language in public. I spoke quietly and firmly to three teenagers sitting in our library not too long ago. Every other word was f***, they were speaking loudly and there were young children with their mothers choosing books. They were very good and stopped it immediately, so I thanked them with a smile. It only needs for us all to make clear what is permissible and what is not. But the mothers there hadn't acted, and neither had the librarians. I suppose I could have received a right mouthful, or worse, but someone has to draw a line IMO.