To feel angry at people running their car/van engines when waiting in car parks?

It's very inconsiderate of people around them. The fumes are disgusting. But I guess as long as they are comfortable, that's all that matters to them.

Sometimes when I've had to wait in the car for a long time and it's very hot or cold I have turned on the car to run the aircon or heater for 30 seconds, just to take the sting out of the air. I don't see that as the same as constantly running the engine, but maybe some people don't like that either. No-one has ever been around at the time though.

Not just you! This is one of my pet hates. When we lived near a school it drove me completely nuts.
I did ask people to switch their engine off when they parked across the end of my drive as I felt I had some kind of bargaining power then, but rarely challenged otherwise unless it was someone I knew.
Reason was usually 'keeping the aircon going', often with windows open too.

Hithere

They may have the ac on while waiting for someone?

No excuse surely. What is even worse, is large tourist coaches, all in a line near famous sites, doing the same- keeping the bus cool for the punters. Totally out of order. In many US National Parks and many European cities, this is totally forbidden and carries very large fines.

"Rule 123 of the Highway Code states, ‘You must not leave a vehicle engine running unnecessarily while the vehicle is stationary on a public road’.

"This is enforced under Section 42 of the Road Traffic Act 1988, with local authorities able to issue a fine of up to £80."

It's the law, but apparently not many people are aware of it.

Last time I asked someone to switch off their engine in an enclosed carpark I got told to F off. I now pick my battles more carefully.
Some people are all me me me.

They may have the ac on while waiting for someone?

‘There’ not ‘they’re’.
Silly autocorrect!

Yes, it is very annoying and I wouldn’t think twice about asking someone to turn their engine off, if they’re sitting they’re parked up with their engine running unnecessarily.

Not long ago, I gestured to a driver to turn his engine off by miming turning a key at him. ?
He looked a bit surprised but understood what I meant and he complied.

Background: I was volunteering at my local Parkrun and the man’s adult son had completed the run and the wife/mum was busy chatting to others and then faffing with stuff in the car boot. Son was sat in back seat and dad was sitting in drivers seat with the Diesel engine running and it was definitely taking minutes rather than seconds.

What really pissed me off was that our little Parkrun is a trail run through woods that starts and finishes in the car park so other runners were still finishing in dribs and drabs running into the car park, whilst this idiot sat with his engine running.

Who on earth wants to encounter choking diesel fumes as they’re finishing a run and probably feeling slightly breathless? ??‍♀️

Yes I agree. Sometimes parents do this outside schools.
Sometimes drivers just sitting texting/speaking on their phones. Best to knock on car window and ask politely to turn engine off. Amazing really with cost of fuel. ?