Talking dirty!?

So last time I had sex with the guy I'm fucking he asked me to talk dirty. I felt so pressured I was like "fuck it, not happening" and literally just stayed quiet. What the fuck does that mean? How do I do it? What am I supposed to say? Is it like "baby your dick is so big" orrrr??? Sometimes he'll call me a slut in bed and I think that's pretty hot, but am I supposed to call him a dirty mother fucker or something? I don't want to sound stupid ahahahaha! I've read so many articles but none actually tell me HOW or what I'm supposed to do.