I did once jump down on to the line on Platform 4 at Guildford with a Down train already running into the platform. A mail bag which looked as though it had something square and solid in it had fallen down between the rail and the platform, and I thought it might damage the shoe-gear. I jumped down, grabbed it, swung it up on to the platform and scrambled inelegantly back; I was eighteen and (too?) keen.
Having lived abroad, I have seen that there does appear to be both a more relaxed attitude to the rules, but a greater appreciation of the risk and the need to use your common sense. There is also, and this extends well beyond railways, an attitude that the individual should act reasonably and responsibly; if they do have an accident through their own stupidity, then it is their own b silly fault and not that of the railway.
Even so, the stupidest I have seen, of a number of incidents, was the chap at Lund who decided to take a short-cut across the tracks just as a fast freight was approaching. He ambled across, making no move to hurry despite the loco horn playing a tattoo, and the Rc was only a couple of metres from him when he got clear of the track. He was sufficiently close to the loco that a backpack or flapping coat could easily have caught the corner of it.