A cleaner left the keys to a bank's front door sitting on top of a cashpoint.
And staff at the Natwest didn't even thank the honest passer-by who found them and returned them safely the following morning, reports the Daily Mirror.
Paul Andrews, 58, couldn't believe his eyes when he spotted the keys while out walking near his home in Pinner, Middlesex.
He said: "I tried them in the door and it worked, so I locked up, put them in my pocket and went home. It's ridiculous.
"They spend loads making sure everything is locked and then someone leaves the keys outside. I'm pleased I haven't got an account with them."
Paul rang the police, but two officers who turned up said: "You could open up for them and hand the keys back personally."
However, Paul said embarrassed staff were far from appreciative the next morning.
Branch manager Kay Patel said: "They're the cleaner's keys. If anyone had gone in the alarm would've gone off. Security would be here in an instant."
But Paul hit back: "I rang the emergency number on the door and left a message but nobody got back to me. I did a good thing and instead of thanking me they were defensive. That annoyed me."
Later a NatWest spokesman said the locks were changed as soon as they were aware of a problem.
He added: "We ask the gentleman to accept our thanks for the safe return of the keys."
Common courtesy is obviously not so common.