More often than not, I just let the guy irritate himself and give him enough room in front of me to do it ......... NOW. Once upon a time, it was a duel to the death and I always won. Always. I was an extremely precise and talented driver; never got a (well-deserved) speeding ticket and never caused a crash nor had one. My skills have atrophied to a certain, but not large, degree; what has atrophied more is the need to fight with 'em. I just let 'em aggress as they will and murmur to myself, "go ahead, asshole, your ticket/accident is up there a-waitin' fer ya". Mostly.
Plus, I have finally hit on adjusting the sideview mirror just right to reflect their high-beams back at them. A little passive micro-aggression, if you will.
Lastly, several years ago, as a Christmas present, Gunsmith installed a dual exhaust system on my truck. Nice low rumble, right? Talk about a loss-of-license waiting to happen. Since then, I've had a small number of truck drivin' fools sidle on up at a light and give it a little gun as, you know, an invite. Shiny, but no dice. But sometimes I'm sooo TEMPTED.