I'm going to jokingly call my gf a stalker because she told me she made a playlist in about me.
Why did she make a playlist about you?
She wanted to hear songs that reminded her of me.
It's fine to make a joke about your girlfriend being a stalker because she made a playlist about you, because it's clear that you're just kidding around. Being playful with your partner is great as long as it's just in good fun.
But I didn't find this funny at all, what if she's planning on killing me.
I thought you thought it was a joke and it is okay to joke around with your loved ones, but if you think it is serious, you shouldn't joke about it. You can distance yourself from her if you think you are in danger.