I'd have brake checked em in a second.
You do that here in Texas its YOUR fault AND you either get a ticket or go straight to jail. Depending on the severity of the accident. At those speeds and them being on bikes most likely you would go to jail, be ticketed for reckless endangerment, attempted insurance fraud, speeding, failure to yeild the right of way, failure to stay right on a highway. (in Texas the left lane is for passing only...not that its enforced all the time but, its still the law)
On a side note, I was passing a car a few weeks ago, I sped up behind another car to get infront of the car I was passing. The guy who was right in front of me did the brake check thing. I was only behind him for a few seconds but he had had a bad day. Got even worse when I flipped him off ( I know my bad) anywho he followed me to my exit. I pulled into a gas station and he jumped out of his car.
He made a few threats blah blah blah. Long story short the cop that saw him do it pulled in shortly and read him the riot act then preceded to ticket him.
It was for reckless endangerment. pretty steep fine on them iirc.