"flash to pass" is internationalese for "get the eff out of the way". It is not illegal in MA. I do not care how fast you are going in the passing lane: if someone is going faster, GET OUT OF THE WAY. What's it to you? No skin off your nose. If you want to control a citizens speed, take the test, get on the job and write tickets. Now, if you are a lemming or a cop not in his jurisdiction, STFU. It's none of your business.
Speed does not kill. Stupidity does. "Road Rage", so-called, happens when one citizen blocks another: GET OUT OF THE IDIOTS WAY! Chances are he'll get bagged somewhere down the line, and if not, IT DOES NOT EFFECT YOU! It is none of your business.
Now, as far as "flashing lights" being forbidden, as Wolfie suggests ("alternating lights"): I don't believe that was the intent of the law, I think it meant wig-wags. I would not want to go to court claiming a violation of that statute for flashing high beams. Secondly, I believe the statute addressing "dimming" ones headlamps says something to the effect of "when approaching" other vehicles. If you are approaching other traffic from behind DIM THE LIGHTS. If I'm wrong on the wording, I'll trust you'll correct me: I don't have a MV&T book at hand...that is just my recollection.