They should shake your hand. They are acting quite strange not shaking your hand and being polite to you at the same time. Do you have some dermatological ailment? The only criteria or reason I would probably not shake someones hand is overt disrespect for Islam. I have numerous Malaysian non-Muslim associates. They are particularly scrupulous and cautious like yourself in understanding what Islam means for Muslims. They would never make mockery of religion or speak ill of the prophet, the Quran or our beliefs. I dont mind criticism but once one notes recurrent sarcasm, displeasure, mockery of Islamic values and practices especially if it has been explained to him in a correct manner that displeases and frustrates any potential dialogue, interaction and association with him.