Meaning
What does Snowflake mean?
A snowflake is someone, who gets destroyed by the mere touch of a hand.
It is a slang expression for people, who are too delicate and vulnerable, so much so that you can’t even touch them, because it is already perceived as an assault.
“Snowflake” today is mostly a political insult to the easily triggered members of the new generations; Millennials and Gen Z kids.
Origin
What's the origin of Snowflake?
The insult “snowflake” has a long and tedious history, twisting around the sticky bogs of racism.
It was first used during the Civil War in Missouri, to pro-slavery people, who only considered whites to be valuable.
More than a century later, in the 70’s, “snowflake” was utilized as an insult to black people, who were perceived to be acting overly white.
Spread & Usage
How did Snowflake spread?
The contemporary meaning of fragility, however came with the 1999 cult film Fight Club, in which the members of the group are disillusioned by a monologue, containing the line “You are not special. You are not a beautiful or unique snowflake.”
The metaphor is clever, because most people consider themselves to be “snowflakes” not because of their own fragility, but rather because of their “uniqueness”.
In 2015, the expression “generation snowflake” had stuck on the new generations, after a dispute at Yale University, concerning “culturally appropriate” Halloween costumes.
Urban Dictionary has a large collection of definitions on the subject: https://www.urbandictionary.com/define.php?term=Snowflake

External resources
- Merriam-Webster – No, ‘Snowflake’ as a Slang Term Did Not Begin with ‘Fight Club’