The driver thought I was nuts to offer him this obviously easy money, and accepted it. I told him up front that the first honk, and the extra money was off the table. He said - ok - and we started the ride. The first few kilometers were pleasant, and the driver was cool with it - but as we entered the business district with more traffic, he became more and more frustrated and started to hum and sing to take it out a bit. Then, he kind of started "barking" (for the lack of a better word) at other drivers who irritated him. He then resorted to outright shouting at the drivers. Eventually, something snapped and he honked once. I told him the deal was off, and the rest of my trip was a veritable honk-hell.
I have always believed the stress ball theory after this one-off experiment.