In my experience it's not so much about hat you say as in how you deliver it.

Example; the bard, who was essentially a noire style mobster, sees a couple of things harassing a friend of the group. He turns and commands the ranger:

"Altis, if the man with the knife doesn't drop it, please pin him to the wall"

This got their attention. The man with the knife slowly turns around.

"Yes, you. Drop it or die."

It was just such a perfect situation that I let them have their fun. The thugs tried one move, but the ranger did as she was told, and pinned him to the wall. The others fled.

So what I want to say is, don't just use the "I am super powerful and edgy" lines. Odds are they won't even take you seriously. Show them a threat they will take seriously, and convince them that you aren't bluffing. The odds that this unassuming guy in robes would raise an army from hell to hunt them down? Eh, just a weirdo. The odds that the buff lady with the giant crossbow could pin a guy to the wall with a bolt? Pretty fucking huge.