How long should the motorist in front of you be allowed to do nothing at an advanced green light until he/she hears the polite toot of your horn from behind? For me, it's the 2nd syllable of "Mississippi" in my 2nd "Mississippi". So, "one Mississippi, two Missis..." and then you'd better be rolling on through. I think that's more than enough time for the synapses in the brain to fire and take action.
I'm convinced that a great number of drivers have no clue what a flashing green light in their face means simply because so many do nothing until prompted from behind. To be clear, when you face a flashing green light or a left-pointing green arrow and a green light, you may turn left, go straight ahead or turn right from the proper lane. This is called an advanced green light because oncoming traffic still faces a red light. Ring a bell? What's even more inexplicable is when the first and second cars roll through and third still stops to assess the situation. By the time it's your "turn", the advanced green has ended and the opportunity is lost. Damnation, I hate lost opportunities.
I don't lay on my horn in these situations, although I'm not ashamed to admit that I've done so in others. A polite couple of taps on it will usually do the trick. It's what I call my "courtesy horn". Usually the driver ahead gets the message and darts on through quicker than normal. I assume they are trying to compensate for their earlier inaction.
Sometimes, however, you get that proud, righteous jag-off who takes your courtesy horn as an insult and either rolls through at a snail's pace, continues to do nothing, or worse.
Last summer, I got the "or worse". The driver ahead of me clearly had no intention of taking advantage of the advanced green. I tapped my horn twice and got nothing more than a long, menacing glower in the rearview mirror. He then slowly proceeded, turning left through the intersection with me right behind. When we were both through the intersection, he switched to the right lane allowing me to pull up beside him. Words were exchanged and he ended the discourse with, "Don't f*ck with me, dog!" I couldn't help myself and laughed out loud at the absurdity of the comment before he sped off.
In hindsight, it wasn't the wisest move considering my wife and children were in tow, but I remain unapologetic preferring instead to use a simple set of criteria to determine who gets the horn. Here's a list of those who might deserve a second thought before using your courtesy horn, or may otherwise be immune to its effects:
1) Cops. One short "beep" might be acceptable. Try two and you're really pushing it.
2) NRA or similar type bumper stickers. Dangerous. In contrast though, those with humorous bumper stickers (Jesus is Coming. Look Busy! is my favorite) will typically give you a polite thank-you wave after a courtesy horn, so honk on.
3) Old, short men wearing hats. They're usually the ones driving an 80's model land yacht. Don't bother with the horn; they likely won't hear it and if they do, they're apt to swallow their teeth and you don't need that on your conscience.
4) Monster trucks. These slack-jawed quadrupeds have an image to maintain and aren't about to let you tarnish it. It's road rage waiting to happen, so holster your weapon.
5) Student drivers. Yikes!!! An unexpected honk from behind may cause Junior to reverse into you. The cop won't understand and you'll just ruin everyone's day. Save it.
6) Pimped rides with tinted windows. You never know how many thuggy little wannabes are going to spill out of these things. Usually not worth the risk.
All others, and there are many, get the horn.