I don't drive so I'm curious why you specified leaving the car unattended? Is double parking fine if you hang around to keep it company?
Double-parking is when you park in the lane of a road with parking alongside it, blocking the people parallel parked AND the flow of traffic.
Parking but leaving it idle with the driver is forgivable if it's not busy and it's quick (i.e. for a passenger running in to grab something from a shop). The driver can move the car if necessary. Parking and leaving the car unattended means the car is blocking the road with the driver unable to move it until they return to the car.
It's a bane of busy cities with narrow streets. Assholes will leave a double-parked car and run in for a 5-10 minute errand. Inevitably some sort of large vehicle comes along that cannot squeeze by the car and it starts an symphony of people laying on their horns, trying to get the driver to come back and move their car.
I've seen shit like this last for 30+ minutes and fistfights breaking out over it. It's disruptive to drivers and the people in the area who don't want a bunch of cars honking their horns.
