I do nothing. I know guys that will brake check, at best, it's discourteous. At worst, that's just asking for trouble.
I pull over if I'm being a slow poke, when it's safe, or after 5 cars or more are stacked up behind I think is the law in California.
Funny story: I was headed up Hwy 50 from the Bay Area, for a short trip to Travertine Hot Springs on New Year's day. We had a lot of snow on the ground, it's 8pm, lot's of slush on the road so I slow it down. There's an Audi tailgating me, likely a snow skier headed up to Tahoe. He rides my ass for a while, then backs off 25ft for a half mile, then back on my bumper. My rig has new BFG All Terrains, I've got a good 'seat of the pants' feel for slippery, and it was, so now I'm doing 35mph in a 50mph zone, like the cars in front of me. It's snowing, you can't see the lines on the highway.
As we gain elevation, it's getting even more slippery. At a wide spot in the road, on a curve, where it goes from our one lane to two, a passing zone. Mister AWD Audi decides to pass me on the left with the infamous "I'll show you!" move. You know the one, the guy misses clipping my rear bumper by inches as he goes around, tugs on the wheel and misses my front fender by a few feet...
Well it seems that AWD Audi's wide, low profile tires are really up to the task, and the Audi's tail steps out a few inches. The guy was doing a pretty good job at first, driving it with the throttle, tail hanging out. I slow down, in case he doesn't gather it back up. But the hot-dog got a little cocky and the car starts whipping back and forth, each whip taking him closer to the gaurd rail on one side, then closer to the oncoming lane and traffic, the other.
I've slowed to 10mph, have a big-ass cattle guard front bumper and a front row seat. Popcorn anyone?
This clown runs out of grip, talent, and real estate at about the same time as he looses it, into oncoming traffic.
The Audi comes to a complete stop, broadside in the oncoming lane, oncoming headlights baring down on him. I figure I'm going to need my jacket, flashlight, first aid kit, me GF has her cell phone ready
Fortunately, the oncoming cars were also going plenty slow, and managed to avoid contact with the A6.