do you think wearing a trench coat will be overly dressed? since people normally wear trench coat when going outside (when they enter events or buildings they'll take off the coat right?)

Phillistines. Those 2 coats in the pictures are nothing close to a trench coat. One is a double breasted overcoat, the other is called a field jacket.

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Added on November 16, 2010, 11:48 pm

Then you are misinformed. Originally trench coats are raincoats made of treated cotton drill so as to make it water resistant. Its primary usage is to filter out droplets of rain water from hitting your clothes similar to your yellow poncho. Of course there are also woollen versions for cold seasons, just like how one should wear flannel trousers during winter, not denim in Malaysia.