Growing instances of ugly Singaporean behaviour have troubled him, said Prime Minister Lee Hsien Loong last night.
These Singaporeans have been "reserving" public roads outside their houses with flowerpots or dustbins so they can park their cars.
They have quarrelled with their neighbours over the washing of common corridors, placing of furniture and noise, and they have objected to the building of elder-care facilities or studio apartments in their precincts - while suggesting they be sited nearby in another estate.
For now, these cases are a minority, he said during his National Day Rally speech on Sunday, but still seem to be part of a "rising trend of not-so-good behaviour". "We seem to be getting less patient, less tolerant, less willing to compromise in order to get along."
This is perhaps due to the disappearance of the "kampung spirit" of old, he said. In the past, neighbours met regularly at common spaces, whether waiting for a lift that stopped only once every three floors, or watching TV at community centres.
Now, Singaporeans lead more private lives and interact less with their neighbours. And "less interaction results in less consideration, maybe more self-centred behaviour".
"We should not let this spread, and make us ugly Singaporeans. I think we will be ashamed of ourselves," he said.
"It's not just a matter of courtesy, but goes much deeper than that. It reflects how unselfish we are, how much we respect other people."
He noted that Singapore's harmonious society has been built on big-heartedness and accommodation, citing the way void decks are shared for Chinese funerals and Malay weddings alike.
Such natural compromises show the spirit of give and take and mutual accommodation among Singaporeans, he said: "We're all in this same country together."
But he also said he has been encouraged by other trends, like the way more young people are taking up social cases.
He mentioned Ms Tok Kheng Leng, 20, a social work student at the National University of Singapore, who mentored other young people and led overseas youth expeditions.
Ms Tok told The Straits Times that, in her view, ugly Singaporean behaviour arises out of the fear of losing out, due to the limited resources here.
But she hopes that more people can see that there is much to gain in giving.
"I'm not waiting till I'm older to volunteer because I think I have the capacity now," she said. "I receive a lot in the process. The youths I interact with teach me a lot too."
Sembawang GRC MP Ellen Lee welcomed Mr Lee's strong words on the topic.
"It's good that he used this occasion to tell these people that this is really unacceptable behaviour, and that, being a small country, we cannot afford such selfishness."