It's wrong to slap someone.
Hilda would slap anyone who mildly annoyed her, like siblings, friends, and even her parents.
Hilda wants to communicate that she's annoyed.
Hilda decides to just wear a mood ring so the color will show everyone she's annoyed.
Hilda keeps slapping everyone when she's annoyed and it just annoyes everyone else too.
Hilda's friends and loved ones are relieved that they won't be slapped anymore.
Eventually someone slaps Hilda back, and they get into an endless cycle until someone force quits the slapping.