(noun) - (1) a wimp, or overly sensitive male who lacks toughness, emotional fortitude, or traditional qualities of manliness; (2) an insult that is most commonly used by the alt-right against liberals, or (3) a reference to the book/movie "Fight Club" by Chuck Palahniuk.
This term was popularized and largely originated in the the book (and movie) "Fight Club" by Chuck Palahniuk, where the protagonist was effectively telling people, "You are NOT a special snowflake." The term "snowflake" may have occasionally been used a bit in the 1970s as an insult to refer to a delicate man, but the term "special snowflake" was popularized by the above "Fight Club" movie.
"Dude. Stop being such a Special Snowflake."
"What? Screw you!"
"You are not special. You're not a beautiful and unique snowflake. You're the same decaying organic matter as everything else. We're all part of the same compost heap. We're all singing, all dancing crap of the world.” -- "Fight Club" by Chuck Palahniuk