Blocking a passageway or exit while using a smartphone is considered ruder than littering or being late, a survey of undergraduates has found.
On average, respondents rated the social faux pas as between "somewhat rude" and "extremely rude". It is also seen as worse than talking loudly on a smartphone.
However, it is not as rude as smoking in a smoke-free zone or refusing to give up a reserved seat to someone who needs it.
More than 235 students were questioned on their use of smartphones, tablets and other devices by a team led by Associate Professor Vivien Lim from the National University of Singapore's Business School's Department of Management and Organisation.
The team wanted to better understand mobile device usage patterns.
Prof Lim said many people are glued to their hand-held devices because they are "afraid of missing out on important events and information".
She also noted that constant smartphone use alienates people from family and friends.
"We often fiddle with our phones and tablets to avoid being looked upon as uncool, or 'social pariahs' - as if being on Facebook or WhatsApp proves that we are socially connected, or that we are socially competent," Prof Lim said.
"In reality, this behaviour hurts rather than helps. The constant use of ICT (infocomm technology) devices not only affects sleep and well-being, it also alienates users from their family and friends, preventing them from connecting at a deeper level with those around them."
Real life, Prof Lim acknowledged in the study, is somewhat more complex.
"We are not asocial, or withdrawn from society; rather, we are an increasingly 'e-social' people, having a strong need to stay connected with others as much as possible through the online world," she said.
Such behaviour was evident among shoppers at Bishan mall Junction 8 yesterday.
Some, glued to their phones, declined to speak to a stranger.
But at a fast-food outlet, a pair of pre-teen siblings pored over a game on a tablet, while next to the Bishan MRT station, a father snapped a photo of his wife and baby daughter on his phone.
Mr Chan Chong Wah, 35, performed his post-run stretches outside the MRT station while checking his iPhone.
The project manager admitted he is occasionally tempted to check his phone while out with friends.
"At some point, it becomes a habit but I acknowledge that and try to stop it," he said.
But Miss Vilasini Govindaraj, 25, who was reading a Chicken Soup For The Soul self-help book at a cafe, said she prefers paper books to electronic devices.
The officer at an immigration services firm said she does use Facebook "but I'm not a person to tweet or say what I'm doing, where I am, all the time... I like my privacy".
As for social networkers having a fear of missing out, Miss Govindaraj remarked: "What are they afraid to miss out on?"