I was always taught that a courteous driver will warn a vehicle being overtaken with a horn honk. Not the "Get out of my way asshole" lay on the horn honk. But the "Excuse me, just want you to know I'm here" single toot.
This is similar to the the double "toot toot" you might use when the driver in front of you doesn't see the light turn green.
My commute is a backroad country drive with an average speed limit of 50 mph. Since I live in the U.S., all the other cars on these roads have terrible drivers, hence my 4 passes a week quota. Sometimes you just have to pass and occasionally I can overtake 2 or 3 at a time, which really helps improve my weekly average.
Now no matter how polite you try to be and do the right thing, the courtesy toot usually ends in four different scenarios.
1. Driver issues an inappropriate hand gesture.
2. Driver accelerates to block your pass
3. Driver tailgates you for the rest of your commute.
and if you're lucky...
4. Driver continues on oblivious to anything buy herself and her phone while completing her journey 15 mph under the limit.
A horn is required in most states to be street legal and can be a versatile driving tool. But with road rage so prevalent it has become a taboo technique. So the question remains. Do you use the courtesy toot? or just make your pass and be on your way?