Mayhem is when someone does something that hurts someone else very badly. It's like when some kids are playing and one of them accidentally hits the other one with a ball and their arm really hurts. But with mayhem, it's not an accident- someone does it on purpose and it can be really, really bad.
For example, sometimes people get into fights and they want to hurt the other person. They might punch them or kick them really hard or even use a weapon like a knife or a gun. This is really dangerous and can cause a lot of harm, both physically and emotionally.
Mayhem can also be when someone destroys someone else's property. This means they break something that belongs to someone else, like a car or a window. This can be just as bad as hurting someone because it can cost a lot of money to fix or replace the broken thing.
All of these things are considered crimes, which means that if someone does them they could get in trouble with the police and go to jail. It's important to always be kind and respectful to others and their belongings, and to never intentionally hurt someone else.