as you mentioned you wanted to wear the vest for a presentation right, what i would do is firstly wear a long sleeve shirt (instead of a short sleeve which you showed here), then i would button up and wear a tie (i see you unbuttoned the top button, bad look for me unless you have a really solid build), then i'd button the vest, wear dress pants and dress shoes.. you'd look more like a gentlemen this way..

edit: oh and one more thing, i'd try to keep the shirt collar within the vest instead of letting them hang outside.. i feel its just a more modern look..

yeah your vest is too big, it should fit snug around your body.. your tie knot looks great btw, spot a dimple there as well =)

i like tucking in my shirt collar into my outerwear whether it may be a vest/cardigan/v-neck sweater/jacket.. yours looks alright now because you fastened the top button, otherwise the'll be hanging out from your vest and you're going to look like one of those russian mobs in the old movies..

That kind of reminds me of Chuck Bass in Gossip Girl. Anyway, those boys in Boys Over Flowers are serious lady killers with their good looks and in their tailor-fitted branded garments.
By the way, how does the korean version fare if compared with Japanese's Hana Yori Dango or Taiwanese's Meteor Garden? I find the Jap one better than Taiwan's but am still deciding whether to download the Korean's.