how do i talk dirty?

ok so my partner gets likes it when i talk dirty to him during sex but i really just don't know how... and when i say dirty i mean like how pornstar dirty talk all kinds of wild and nasty things, he just likes it but for some reason i just don't have that in me. most the time he just kinda tells me what he wants to hear me say and i'll just repeat it but other times i can tell that he just wants me to say things without him guiding me and i just won't know what to say at all, idk what it is about it that i kinda feel so uncomfortable about... how can i learn to talk really freaky and dirty to him? any tips?