I think it's bad manners to put feet on seats, even though there are many signs in the carriage, the said person isn't the one having to clean them.
If on a packed train and having to stand, why do people, especially teenagers listen to music at full volume with headphones on and all in the vicinity can hear is boom boom!
It also winds me up when you turn up e.g. at Preston for a Virgin service that has started further North to find someone already sat in your reserved seat, they won't move, with the words of "It's my right" and even worse when they haven't a seat reserved!
I will stop there, I don't want to get my blood pressure up!