to quit, esp. from fear; to chicken out or back down as from intimidation;
scared or frightened to act; back down from a confrontational situation because you are too afraid to act.
After being challenged, he punked out.
You just got punked out! (=You walked away or retreated after being challenged, or verbally abused or disrespected.
The common practice of 40 year old mothers across the US. The art of correcting a young person's grammar, mid-sentence, in front of large amounts of people, most likely the young person's close friends.