Safety, safety, safety!!!
Having just traveled from Michigan to Florida and back with my RV, I have seen almost everything mentioned in these posts, and more. That said, please keep your patience and do not add to the carnage by trying to 'educate' those idiots. Horn blowing will confuse them, riding their bumpers may cause them to take unpredictable actions, weaving at them may cause them to dart into the next lane, i. e. as one must admit, these drivers are obviously less then competent, and if their actions only hurt themselves one might be able to justify your response, but usually there is a good chance they may injure or kill innocent parties.
So you excellent drivers need to have patience with the idiots and even drive for them by keeping them as safe as possibly with proper spacing and even a little protective blocking, the life you save may be your own.
Now for the amusing part, just last Saturday I was at my wife's family reunion where three of her uncles were telling me they liked driving in the left lane because it was smoother out there. And were upset that a nephew had been stopped in Florida for 'spending too much time in the left lane'. Good thing their truck driver youngest brother was not there, or they might have gotten two 'ear fulls'.
Then one mentioned that he wished he could drive as fast as he could on the autobahn in Germany. He had no response when I told him I have driven 180 mph on the autobahn and still got passed like I was standing still. And that they enforce the 'no passing on the right' laws!! So you had better get over before getting a bumper in your 'boot'. Maybe requiring $240 for a drivers license in Germany is money well spent, as it does improve the driving somewhat.