I've done roughly the same once, hotel room, husband watching, ...
It started slow (vanilla sex), but as soon as the husband came in, the woman started ordering him around and verbally abusing him. She started to encourage me to do the same, so I did. I started the dirty talk and fucking her very roughly. I said things like "I'll show you how you have to fuck a dirty slut"
I think it will come naturally because at first I didn't know it was going to be something like this, but as it turned out after her encouragements I became a dirty talking machine.