acquired taste

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One that is unpleasant on immediate experience or is likeable only after being experienced repeatedly.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A taste which is not natural or innate, but which has developed through habit or learning.
• noun idiomatic Something that is appreciated only after having initially been regarded as unappealing or unpleasant; a person who is regarded as difficult or dislikable but of whom at least some have grown to approve.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a preference that is only acquired after considerable experience