I'm sorry you feel that way.
My apology, whether it is required or not, though, does not in any way justify direct action from you if you are driving a car. Sure, if you want to stop along the road and shout a few expletives, go right ahead. If you want to argue that I am wrong and you are right, feel free. Everyone has an opinion (including me) and if you feel the need to share it, that's fine. I probably won't agree with it. I'll probably tell you where you logic falls down, but that's all good and dandy.
What none of this does, is excuse you trying to frighten me by hitting the horn as you draw alongside, or drift your car towards me. Even if only slightly.
I am made of flesh and blood. I am about 85kg. My bike weights about another 10kg and my bag and clothes perhaps another 7kg. about 100kg in total. That 100kg is surrounded by air. Nothing else, just air.
When you feel the need to make a point, and you feel the need to make that point as you are passing me too close, and moving closer towards me, and you are hitting your horn, remember that that 100kg of unprotected person, bike and personal belongings, is up against you in your 1000kg of car. Remember also that that 1000kg of car is mainly made from hard metal and glass, metal and glass that have been designed to protect, not me, but you. You have crumple zones, air-bags, ABS, ESP, and many many other safety features that will keep you safe.
What do I have? I have my wits, my experience of cycling on the roads, my knowledge of particular road trouble spots and a wee bit of plastic on my head. Even that wee bit of plastic doesn't really provide any protection (it just provides somewhere to put my camera) and it certainly doesn't protect me against 1000kg of car.
So, when you see a cyclist up ahead making a friendly gesture to a driver that has just passed him, asking him to give him a little bit more room next time he passes, don't take that as a personal insult. Don't fall back into the 'bloody cyclists' rage that burns within you. Imagine yourself in my position, and ask yourself, am I gesturing to drivers to piss them off? Am I riding that far out of the kerb just to bring about confrontation?
Ask yourself, who would win when it's 100kg against 1000kg?
I'm just trying to get home as safely as I possibly can, and perhaps trying to enjoy the process at the same time. So please, don't do this.