I gave up booking in the Quiet Coach, as there always appeared to be one woman so engrossed with her own inane conversation that she hadn't realised she was the only one talking
On one occasion, I did helpfully point at the "Quiet Coach" sign, but she said that didn't apply to people talking. It didn't help that she had already had a long noisy conversation with the catering staff when they came through.
Other (rare) interventions have usually elicited the response that "that's where our seats were reserved" or "oh well, were sat here now" from a family with two kids
So now I find it less stressful to sit in the Unquiet Coach!
(Bring back the smoking coach, where the atmosphere was much more relaxed, if a little smoky)