Never understood the purpose of beeping your horn at someone who has stalled their car. Most likely thing you're going to achieve is to make them more flustered than they are already, meaning they'll take longer to get their shit together and drive off.
If people are beeping to say, 'you're not supposed to stall your car' well that's a statement of the fucking obvious if ever there was one. I'm sure someone has deliberately stalled their car at some point in human history but I reckon it's a good 3, 4 million times rarer than people stalling when they didn't intend to.
Only time I'll honk is if someone stalls on a hill and then forgets to put the brakes on. In that situation there's actually information that needs to be conveyed to the other driver, namely 'your car is rolling backwards and about to hit me, please apply the brakes at your earliest convenience'.