that's ok! You can also say: Я не шучу

I'm not sure if 'to joke with...' has this meaning: "kid., v intr.: .... 2. To deceive in fun; fool: I could only hope they were kidding me when they said my car had been stolen." But it is this, specificaly. btw, does 'joke with' mean the same?

You can say: I mean it! I'm serious! - Я не шучу! Я серьёзно! Это не шутка! - It's not a joke! Я не шучу с тобой, я тебя не разыгрываю! Это не розыгрыш!

right, also could be translated as "I'm not playing with u"

"Я тебя не разыгрываю" or "Я не шучу" or "Я серьёзно" or "Никаких шуток"