That moment came today.
It wasn't anything blatantly bad (and I've certainly had to deal with Mr. Toxic in my classes before---today's issue was not even in the same universe as that). It was basically two overly-chatty young men in the front row who were just a little too disruptive to the class. Now normally, I'm ok with a little bit of chatter, when it's students clarifying points for each other or asking "did you get that?". That's fine, as long as it's kept discreet and short. This was neither. This was prolonged and obvious.
My first strategy in this situation is to stare directly at the chatters and say loudly "is there a question?" This is usually enough to mortify one or both participants into silence, or if not then they're usually bright enough to know that what I'm really saying is SHUT UP ALREADY and they comply. So of course I tried that, and it had no effect.
Because I was still trying to assess the situation (clueless freshmen or testing-authority freshmen?), I stuck to more subtle forms of shut-up-please strategies for the rest of the class period: standing directly in front of them while talking to the class,
Figuring out what to do in this situation is always tricky. I suspect I will see what happens on Wednesday, and step in more quickly if I have to. I suspect I will have to talk to one or both chatters after class and let them know what's acceptable behavior and what is not. I just have to figure out what's the best way to convey to them that I may look like Dr. Nice Gal, but that doesn't mean that they don't owe me the same respect that they give to their other professors. And I have been known to turn into Dr. Raging Mean Prof when pushed too far. And that they really don't want to go there.
We'll see how it goes.