When Eevee evolve into Glaceon they mold into a more reserved and graceful personality. Not unlike a snowflake — as beautiful as they are fragile, they cannot easily tolerate a person's touch without melting.
The "coldness" can range from an evil, icy heartlessness like the White Witch, or just a normal, relaxed and calculating coolness. They as a species are famously aloof, and they also sometimes have a haughty/special snowflake sort of cold arrogance, and thus are difficult to get close to.
Their need to be in a cold environment coupled with their automatic bodily production of coldness further isolates them, as most people do not like the cold and Glaceon find it intolerable to be outside when hot and thus shut themselves away physically in addition to emotionally. Some are even semi or fully nocturnal so as to help keep cold, exacerbating the problem of rarely being around other people further.
But there's nothing COOLER than a Glaceon who is mentally healthy and composed. They are the sunglasses-wearing type of cool.