Not know any better
Definition 1 of 2
Pro Tip 1/3Context Clues
Look for context clues that indicate innocence or unfamiliarity with norms. 
She walked into the men's room by mistake; she didn't know any better.
Pro Tip 2/3Age Implications
Often used for children or young people who are still learning social rules. 
The toddler grabbed the dog's tail—he doesn't know any better.
Pro Tip 3/3Not Ignorance
It implies a lack of knowledge, not the unwillingness to learn or understand. 
He interrupted the meeting, not knowing any better about the protocol.