haha at the yanks. The drunken moron was a drunken moron but there is a lesson here for the pompous cycling advocate too.
The horn is for warnings of imminent, immediate danger only, it is not a communication device for any other purpose, none. It is not there to get someone's attention to tell them you witnessed their bad behaviour. It is not there express your frustration. Using your horn in the manner this guy did was in very bad form and he should know better. He should also know from his own experience the possible reaction from horn blowing is anger & irritability borne of being made afraid for no reason. Couple that with ignorance and drunkenness and this is what you get.
He should have said something politely out his car window or left well enough alone. ****ing moro, ain't a cop, ain't an authority figure, ain't supposed to be out blowing his horn at people. He can be out lecturing people if he's feeling ******y, but the horn is a way to get people to jump and this provokes anger, justifiable anger that can lead to unjustifiable behaviour as witnessed here.