Roman Parking Etiquette

We've stopped at the bar for a speedy breakfast. There's no parking space outside so we block in an already parked silver car and hurry in, leaving the car unlocked. We gulp down a quick coffee and scoff a cornetto and pay. On leaving we notice that our car is no longer blocking in the silver car but is further down the road. "Oh, someone's moved the car" observes E mildly. Then we see the silver car pulling out onto the main road. The driver gives us a big, Italian 'what could I do?' shrug and rolls down the window. "Sorry" she shouts "I waited a bit but no-one came so I had to take off the handbrake and move it". "Don't worry about it" shouts back E, waving as she drives off. We walk towards the re-parked car. "Well that's not really on" mutters E in injured tones, "everyone knows you're meant to sound your horn for a while before trying something like that".