The Secret Cyclist: dealing with intimidation on the road

People shout at me from cars when I am cycling. Not every day, not every motorist, but enough for it to be more than isolated incidents. I do a quick calculation when someone shouts at me or gives me a 4-second blast of their 110-decibel car horn. Is this someone out looking for confrontation or an otherwise law-abiding citizen who is just frustrated by my presence or actions? The vast majority of the time, it’s the latter.
I have a genuine interest in engaging politely with someone who has shouted or attempted to intimidate me. In my experience, most abuse occurs when a driver is ‘stuck behind’ me. Average vehicular speeds in Irish cities are incredibly low due to congestion (less than 10kph in Dublin city centre) but a lot of people see red while behind a bike travelling at 15-25kph.