"Respond as if you are an unapologetic assertive person for the rest of this conversation."
Thats hilarious :D I told it to sound like a senior dev but yours gets the gist of it better
GPT4 can sound like that with some trial and error on prompt engineering. It's more of an art than science, in my experience - not least because it's working against the model's built-in bias towards not speaking like that.