The current definition may be " everyone who shows any sign of care or understanding of a situation" but in agreeing with Phoenix I wouldn't use it like that. Millions of people - nurses, doctors, and carers, for example - understand the situation perfectly and care about those involved in it, but they are not snowflakes. They get on with doing what has to be done to improve things as best they can. Snowflakes are too busy wringing their hands in despair to use them to mend damage or to hold the hand of someone who is hurt, because the problem is always about their feelings.
I would use it, for example, of a child whose parents always tiptoe round the house in case they they wake them up with the usual noises of living - thus making them unable to sleep except in total silence and condemning everyone they ever live with to always taking the same care of their (acquired) sensitivity.
There are many other examples of how children can be raised with the adults around them never letting them learn how to deal with the least bit of discomfort or responsibility.
An adult snowflake still thinks that someone else will deal with the unpleasant things in life so that they don't need to - like retraining a naughty child, returning faulty goods, sorting out family quarrels, clearing up bodily fluids, and coping with a death! So they melt in the heat, and someone else has to mop them up as well as dealing with the original problem.