Have we nothing left in the tank except to grass up neighbours?
So it served us right when, with the orange light flashing dangerously on the borrowed Fiat Punto - emblazoned with the garage's name and logo - we stalled at the traffic lights.
Not any old traffic lights. These were on a roundabout - think Cardiff's equivalent of Spaghetti Junction.
My husband, more used to being half way up a motorway to watch Cardiff City play when anything like this happens, was horrified at being caught in a mini- crisis.
He was driving and gawped across at me when, every time he urgently tried to restart the engine, I repeated, 'It's run out of petrol. It's run out of petrol.'
I've never seen him move so fast. Clearly having quickly assessed that it would be far less embarrassing to stay with the car, he volunteered - or rather announced - he was going to fetch petrol.
'I'm not saying here,' I said.
'You are,' he replied.
This went on for some time as cars flashed past, horns beeped, and I rued the fact I wasn't a sensible citizen who had dutifully put a tenner in the courtesy car fuel tank.
Add to this the fact we had crammed a large set of home-assembly bookcases into the back of the car - the kind of thing that might yet appear on Police, Camera, Action! with the voice-over, 'These people thought they could get away with obscuring the driver's rear vision' - and the situation was what my mother might call 'all hells bells'.
Within seconds, Mario was but a mere flicker in the distance, darting between the oncoming traffic as though he was auditioning for the new James Bond. I decided that it would be most sensible to stay outside the car and alert anyone approaching that the inside lane was blocked.
At first, it was OK. People were moving effortlessly into the middle lane, casting the occasional sympathetic glance. Then there would be a surge of traffic and a bit of ducking and diving as cars tried to keep with the flow.
But, after a while, I started to scan the horizon, affecting a fixed gaze which suggested help was on its way. At one point, I sat on the grassy slope, my linked hands looped over my knees, trying to look laid back. (Only the most perceptive would have noticed the movement of my lips as I silently cursed the vanished Mario).
The thing is, it might be fashionable to say society is turning the other cheek, but I had to start looking determinedly away from the traffic because people were slowing and tilting their heads forward as though they were keen to help. One driver even beeped the horn to ask if I was all right.
By the time Mario strode up, carrying the petrol can like the Budget Box, I was almost in tears.
'What's up with you?' he said disgustedly, as though it was he, and he alone, who had saved us from disaster in the nick of time.
I tried to explain, but he just thought it was me attention-seeking.
This week, I was reminded of people's kindness when I heard that everyone is being encouraged to call a confidential DVLA hotline to shop anyone without car tax.
I hope Britain isn't going to be encouraged to turn into a nation of snitchers, because it won't suit it.
I hope people don't stop being spontaneously kind and instead feel they've done their bit by phoning to grass someone up. Of course, it's being helpful because an uninsured car is a dangerous thing, but how constructive is it to engender the notion that telling on someone is admirable?
Will Britain become a place of twitching net curtains and anonymous voices on the end of a telephone?
Instead of encouraging good deeds, will grassing on people be seen as the 21st century's answer to being a Good Samaritan?