From the Urban Dictionary:
Snowflake children typically grow up to be teacups: easily chipped, cracked or broken. Unable to handle the hot coffee that makes life worth living.
Me, too. Having a tantrum and chewing out someone else, then trying to justify it by saying you were "going all mama bear" really diminishes the speaker in my eyes.
Mama bears protect their cubs from physical danger such as man or other preditors. If/when your child is in danger from a rabid animal or about to get run over by a car or is being spirited away by a pedophile, then the phrase "going mama bear" would fit.
Having a hissy fit and chewing out a total stranger because they couldn't tell if your child was a boy or a girl? Calling a teacher and screaming at that teacher for 15 minutes because they forgot your child ate only organic food and the teacher gave them a chocolate treat on Valentine's Day with all the other children? Or raging into the Principal's office because a school bus had a fender-bender accident and a neighbor gave your child a ride home from that accident? Sorry, that's not "going mama bear".
That's called not being in control of your emotions and lashing out because, once again, life has proven that the world doesn't revolve around you or your child and the entire planet (or even your immediate circle) doesn't always live by the rules you think it should live by.
Or exibit A:
a teacup adult.