Snarky is used to describe a person's attitude. Snarky means to criticize someone in a rude way, usually to hurt someone's feelings. Idiosyncratic means to have strange, peculiar, or unusual habits or behaviors. Snarky is very common in daily conversation whereas idiosyncratic is not. Idiosyncratic isn't commonly used in daily conversation because it is almost too formal. Instead of idiosyncratic, English speakers usually just say odd or weird when discussing someone's habits and behaviors. However, I will try to give a couple of examples!
Ex: She was being really snarky to me.
Ex: I don't like your snarky attitude.
Ex: That person is very idiosyncratic.
Ex: He has some very idiosyncratic tendencies.