[Boromir88]

The coat was made before the whole dwarf-capturing incident so the dwarves would've been happy to give Thranduil the coat (for a hefty price, of course).

Ok, I see, but even with that in mind I would think the feud between Elves and Dwarves would still be going on. Especially amongst the Mirkwood Elves, with Thranduil despising dwarves so much. Now with Galadriel, being Noldor, has a connection with dwarves (Aule), which is why we see her sympathize for Gimli. Celeborn having connections with Thranduil, and being Teleri, we see him a little more "rude" to Gimli, but he does apologize after Galadriel corrects him. Elrond has always welcomed Gloin in Rivendell, and there is no reason for not welcoming Gloin's son either. That pretty much sums up the dwarves vs. elves feud.

Thinking about Thranduil, and I'm trying to think, before he imprisoned them, what would a reason be that he despised dwarves? Here's an interesting quote from Appendix F...

But [dwarves] are not evil by nature, and few ever served the Enemy of free will, whatever the tales of Men may have alleged. For men of old lusted after their wealth and the work of their hands, and there has been enmity between the races.

Now this is talking about the "tales of men," but as already said Thranduil had a great desire for wealth, and jewels. Being that he lives in Mirkwood, and seeing that the dwarves are away with their own riches and gold, he too might have gotten jealous, and he too might have made "lies." This is just pure speculation though.

made for some young elf prince long ago.

I don't see how Thranduil would know that this "vest" was made for some elf-princeling long ago, it was just that "particular vest." I don't have The Hobbit handy, but Elianna (or someone else), would you mind giving the entire quote, it could be important. Maybe, Thranduil was saying, that wonderful vest should be for an elf-princeling long ago (back in the day of the elves, remember in the 3rd age the Elves began to decline) and not worn by a hobbit who associates himself with dwarves. However, I can not tell what Thranduil means if part of the quote is missing, and we still might not be able to tell.