Yes, you should be ashame. You saw that happen in front of your own eyes and yet done nothing about it. Its the "Malaysian Culture" we have in our society that is making us ashame. Yes, you should not throw rubbish into parks, and yes, your are responsible to tell someone else not to do it too. if you expect change, you have to do it youself and make sure that problem does not happen in front of your eye and yet do nothing about it. Don't expect everyone to know their own responsibility, as a individual you make sure people know their responsibility. Look at all the post above, all accuse something else. Make it your responsibility, when you see someone doing something wrong, go ahead and tell him/her it is wrong. when he/she throw something in front of you, you don't pick it up and throw it away. Pick it up, walk to him/her, ask her to throw it in the dustbin. Its your responsibility to make sure people know their responsibility, not take over their responsibility. Like that, why don't follow them arround whenever they throw rubbish you pick it up and throw it into the dustbin. Think Aloud.
When i was in australia, if you throw one rubbish on the street, people will walk up to you and ask you to think what you have done. Does malaysian has the gut to do it? Are you brave enough to make known of people's responsibility? Think and Act.