I've done IV ket in a train toilet quite a few times. Came round on the dirty floor a couple times lol and once with a massive bump on my head.
Normally had to wait until it stopped at a station to actually do the shot, like the poster above said its not ideal on a shaky train. I spilled quite a few spoons while preparing the shots.
IM on the other hand is doable while moving.
More than once blacked out and when I came round gathered my shit and got out of the toilet to check how far away from my stop I was I had missed it and then had to pay extra to get back where I wanted to go.
Not my proudest moments.
IV mdma is one I am yet to tick off my list, train or not. Although it doesn't tickle my fancy very much.
Kinda off topic but I've done shots of K on the back seat of the top floor of a double decker bus before, not even in a toilet, under a camera too. With quite a few people around.
I was in a really bad mood that day.