My(23m) girlfriend(20f) wants to be insulted by me but I can't bring myself to be mean to her

I'm a really nice guy according to everyone, labeled as meek and polite. But recently, my girlfriend opened up about something and told me she wanted to be insulted by me specifically and has been begging me to but I can't bring myself to even call her stupid. I asked her why she wanted me to and she replied that she just wanted to hear it from me, but she hates getting insulted by others and I'm afraid to hurt her, I'm unsure how to even engage it but I only want to make her happy.. I'm not exactly uncomfortable with her desires, but I just don't know where to start and how I'm supposed to insult her.

Where do I start?