It might seem rude to pass gasses but in actual fact you
couldn't really keep it in. It's a very spontaneous action so
usually it would be rather too late to find an empty place to do
it. The noisy ones are usually smell free while the quiet ones that
are the killers.
People passed gasses not because they enjoy doing it but due to
stomach problem. Some people have bad digestion or because they
suffer from IBS which usually produce a lot of gas and 'suay-suay'
it so happened they passed out while in a crowded place. I could
bet with you they would be rather embarrassed with their behavior
too.
I used to teach in some exercise class and this lady would always
pass gasses but we didn't get angry or annoyed with her because we
knew of her condition. In fact I encourage her to go ahead and let
loose should the need arose because some posture we practised
tended to move her bowels and help her greatly in letting go those
trapped gasses in her. But she was very 'jitong' for she would
station herself farther away from the rest of us.
That said I hope we could exercise a bit of tolerance for these
people who tended to pass gasses not because they wanted to but due
to their conditon.