after reading all the posts....
before giving seat to senior citizens, pregnant ladies, or
handicapp ppl, or those who need to be seated, try to observe their
behaviour first, whether they are hunting for seat or they are
standing in a stable manner. Experienced this before, offer seat to
them, they did not want at all, never say thanks too.
Signal to those who want the seat and then give way to them, there
are many kinds of ppl in the world...
Anyway once you are seated, you have the right to remain
there...whether give way to others, its up to your discretion,
although a old man was standing right in front of you... 
Remember one time, was in MRT, i was reading paper, did not look
here and there, the train was full of ppl. Suddenly heard a lady
voice, anyone would like to give way to this pregnant lady? the
pregnant lady face was red immediatly, the lady has no relationship
with the pregnant lady. Was this so called 'kapo'? Since noone
offers their seats, i stood up...hahha...
