This thread is making me think about when I was on a train from Brno in the Czech Republic to Vienna about a month ago. The compartment I was booked in was full, 3 single men (including myself) of varying ages and a mum, dad and child (must’ve been younger than one). Despite the journey being less than two hours the child would scream and scream until she got to watch a video on an iPad - both were annoying to the 3 others in the compartment.
As for the autism thing I’m hearing, I’m highly, highly sceptical. My ex (diagnosed as an adult) frequently got overstimulated by exactly the behaviour this thread is talking about, and we often had to move carriages because of people playing music to loudly (occasionally we spoke to staff, but rather than confront they just told us to move - a difficult feat given my ex is wheelchair bound).
I think that this behaviour should be confronted head on by rail staff (with security as backup) along with plenty of posted notices, especially on longer distance routes.
I’m only 21 but the change since Covid that I’ve noticed has been startling, when I was a younger teenager or a boy travelling from Yorkshire to North East Scotland with the exception of the occasional hen or stag party, the HSTs were often very quiet.