Got told off today by a rather pompous middle aged gentleman in coach A on a GWR. Was travelling back from Paignton with my London friend who I only see about once a year, after a lovely few days break, and we were just chatting, not shrieking, giggling or even talking particularly loudly. He came to us from two rows of seats in front of us and told us he could hear us talking, and didn't we know it's the quiet coach. I was all set to point out that it's not the 'silent' coach, and generally applies to electronic equipment and phones, not normal conversations, but my much more diplomatic friend said "oh we're sorry" and nudged me not to make a big deal of it. I was still annoyed though. I did give him a look as I got off at Taunton.
A young couple got on at the next station after this incident and sat two rows in the other direction from him, and were literally just almost whispering to eachother, and he stuck his head over the back of the seat and told them off too. They looked incredulous. They got off at Taunton too and could hardly contain their giggles as we waited for the doors to release. It really was an absurd reaction on his part. I bet he's great fun at parties!
I didn't think it was forbidden to have a normal level of conversation in a quiet coach. Some people obviously see it differently though.