A hypersensitive, irrational person who can't stand to have their world views challenged, or be offended in any perceived or even slightest of ways; they will have any number of emotional reactions: impuning character and/or motives, blocking on social media, shouting, interrupting, threatening, assaulting, etc. They often live in an echo chamber of their own beliefs and surround themselves exclusively with people and opinions that agree with their own. This term is most often use to describe people left-leaning people, but can be applied both left and right wing people.
I told that snowflake that I respectfully disagree and had some questions, and she started screaming that I was a nazi.
John Doe saw that I agreed with Jane Doe on an issue, and he blocked me; I never knew he was so petty snowflake.