I join the chorus to say I too was surprised to learn...
That some people don't answer the door or answer their phones.
That some people wash their sheets and towels crazy often.
The childishness of adult friendships - people feeling snubbed in the school run, upset that they have been ghosted, seemingly to have really high expectations of friendship from others and if they're ignored it's a huge issue, rather than they just assume the other person is just getting on with their lives and not thinking about them.
A meta-one about threads and mumsnet itself - I am surprised how much people focus on a concrete detail of a thread, and are unable to follow an argument where the issue is abstracted to a principle. It means some threads just go round and round, keep getting dragged back to the first points, and don't ever get to a more interesting or developed discussion.
Relatedly- How many people read the OP, then jump to page 9 and write their bog standard reply "I also don't like grapes so you are not unreasonable to be upset that DH bought grapes". Not interested or caring that there have been 12 OP posts over two days since then, the thread has moved on, OP has now fled the marital home, MIL is in A&E with grape poisoning, DH has been arrested ... we have learned a million reasons why grapes aren't really what the thread is about.
Even on this thread I read everything before writing this post, to make sure someone hadn't already made my point - when I see my point has been made, I don't post!