It's all the tiles in the MTR stations....old guy probably thought he was in an oversized loo!
Having suffered from the gloriously named Faecal Immediacy Syndrome (i.e. when you need a shit you really need a shit NOW) I should have sympathy for this guy but really - shit yourself before shitting in the MTR.
As to the question as to what to do if you are on the MTR: get off at the next stop and ask to use the toilet. Get to know all the locations of all the toilets on the route you use. I knew most of them along the Island Line.
I've certainly had some emergencies in my time and had to "go" without a toilet - but that was always "in the wild" or at minimum behind a tree (actually on a main street in Roturua... but at least in a bush!) - I cannot imagine pooping in an MTR. Particularly when you can (and I have, with my level of non-existent Cantonese) ask the staff to use theirs.
guys...guys....if you really need to go....just find the nearest cha chan teng. There's always one just round the corner. Surely better than pooping in your pants.
i have seen a mainlander woman getting her young kid to pee in a plastic bag ( they were next carriage, but only around 5 meters from me) on hung hom platform ( which has toilets on every platform, surely no excuse), they were waiting for a train, kids says something and holding his private parts, the mum brings out a bag, the kid pees in it, there bins in the platform as well, but they decided ignore the toilet and the throwing the bag in the bin.
the trains pulls over, they hop on the train with the nice red plastic bag full of piss, then they noticed that the train was going to lok ma chau but they needed to go lo wu ( and probably wanted to seat for the entire journey) whilst in the train, then hop out of the train without the bag of piss, which I presumably left under the seat or next to the door. I was pretty gobsmacked and felt sorry for the poor bugger who may step on an burst the bag of piss accidently
There is a HK toilet android app that has proved useful for me a few times. Its all in chinese but easy enough to use and tells you how many meters to the toilet and arrows pointing which direction to walk in