Dave is using the term based on the right-wing political wave in the US. It is used as a derogatory label and personal attack on people, typically when they have no ability to have a logical debate with someone.
Here is Wikipedia:
Generation Snowflake, or Snowflake Generation, is a neologistic term used to characterize the young adults of the 2010s as being more prone to taking offence and less resilient than previous generations, or as being too emotionally vulnerable to cope with views that challenge their own. The term is considered derogatory.[1][2] It is one of multiple examples of usage of the word "snowflake" to refer to people.
Another from Wikipedia:
Snowflake as a politicized insult is typically used by those on the political right to insult those on the political left.[15] Jessica Roy, writing for the Los Angeles Times, says the alt-right in the United States describes those protesting against Donald Trump as "snowflakes", using the term as a pejorative.[16] A 2017 article from Think Progress commented: "The insult expanded to encompass not just the young, but liberals of all ages; it became the epithet of choice for right-wingers to fling at anyone who could be accused of being too easily offended, too in need of "safe spaces," too fragile".[17] Jonathon Green, editor of "Green's Dictionary of Slang" points out snowflake is an unusual insult in that it calls someone weak and fragile without using misogynistic of homophobic references.[18]
Here is Wikipedia:
Generation Snowflake, or Snowflake Generation, is a neologistic term used to characterize the young adults of the 2010s as being more prone to taking offence and less resilient than previous generations, or as being too emotionally vulnerable to cope with views that challenge their own. The term is considered derogatory.[1][2] It is one of multiple examples of usage of the word "snowflake" to refer to people.
Another from Wikipedia:
Snowflake as a politicized insult is typically used by those on the political right to insult those on the political left.[15] Jessica Roy, writing for the Los Angeles Times, says the alt-right in the United States describes those protesting against Donald Trump as "snowflakes", using the term as a pejorative.[16] A 2017 article from Think Progress commented: "The insult expanded to encompass not just the young, but liberals of all ages; it became the epithet of choice for right-wingers to fling at anyone who could be accused of being too easily offended, too in need of "safe spaces," too fragile".[17] Jonathon Green, editor of "Green's Dictionary of Slang" points out snowflake is an unusual insult in that it calls someone weak and fragile without using misogynistic of homophobic references.[18]