When someone likes something peculiar or different
An example of an idiosyncrasy would be a Hipster
The occurances of two people saying or thinking the same thing or idea, usually of a idiotic fashion.
Stoner Billy and Stoner Kyle were both sitting on the couch when they both said, "Wow...this couch is really soft." Creating an idiosyncrasy between the two of them which would be their topic of conversation for the rest of the evening.