What's "I mean it" mean? When can I say "I mean it?"

Native speaker’s answer
Rebecca
"I mean it" means that you're serious or that you're telling the truth. You can use it when you want to convince someone you're telling the truth or being serious. Like if a friend isn't taking you seriously, or they think you're joking about something. It can also be used to emphasize that what you say has meaning. Ex: You're a really great cook! I mean it. Ex: I mean it, Jimmy. I'm going to take away your allowance if you're naughty.