The general idea is to gain as many miles behind as many locos as possible. Its almost a game. He who achieves the highest mileage wins. Some people are loyal to a particular loco, others to a type of loco, and will aim to travel behind every single member of that class of loco in a set amount of time.
The bashing game often involves leaping off of a train, running over the footbridge or across a 16 track concourse, and barely making onto another service, of which of course contains a loco that you desperately need to clear the set! Sometimes you will need to do overnight 'moves' and rely on information given to you by a fellow basher, or maybe a friendly railway employee who has a genuine interest in trains.
You are of course at the mercy of the railway, and may find yourself arriving at a station in the middle of nowhere and looking to jump onto another service of which is due to leave 5 minutes after your arrives. But you train is late and you sprint over the footbridge, only to find the red tail light of your intended train disappeaing into the distance! And of course, on the front will be the loco that you ever so desperately need.
I can imagine the commuter routes and NEC are ideal 'bashing' locations. And of course, a 'railpass' is essential.
Some 'bashing' phrases for you to use:
Detonated: Missing a train by a matter of a few seconds.
Caped: A service that is cancelled. ie the 1230 to New York is 'caped'
Bowled: Being caught out by a different loco than the one you thought would be heading your train.
Chung up: Being excessed by the guard because your rail pass is not valid on that service.
Flailing: Leaning out of the window, arms waving, usually at the sight of a lineside photographer.
Bail out: leaving your train for the sole purpose of catching another.
Have fun
Not much variance as far as passenger service is concerned.
My friends and I do a sort of 'bashing' with SEPTA, I guess. We always cheer when we see car 269 (and are sure to mention to each other when we get to ride it)--that's the only one which still has Pennsy letterboards. It's one of the shabbier cars in the system on the inside, though
But since it's an MU, it's also a loco, sort of, so maybe it counts for 'loco bashing'
Maybe if there were more variety, there'd be more 'bashing'? It sounds fun.