A stoolie is a person who tells the police about the bad things other people do.
The word stoolie can make people think of betrayal and dishonesty.
Examples:
The stoolie told the police about the bad man.
I don't want to be friends with a stoolie.
The stoolie is not a good person.
The stoolie always tells on everyone!
The stoolie told the police about the stolen cookies.
The stoolie's friends don't trust him anymore.