Hi guys,

Somehow I can't decide whether "rat someone out" means to fire someone from the work or whether it means just betray your college in the work. I came across to this phrase in this context: Girl in a hospital found out about a scam of one orderly guy. He answered her:

So, what, you gonna rat me out?

What pisses me off that I didn't find rat out on the freedictionary.com. That's why I don't know what it is..:-(( From the context I feels that it means So, what, you gonna tell it to my supervisor/ you gonna betray me??? But I'm not sure.

thanks in advance.

You're right. Rat someone out means to betray a colleague. It is most commonly used among criminals. Another common term is "stool pigeon".
perfect. thx.