With the aid of a wooden stool, a fun hat, a shiny carpet and some Canto-pop music, they invited passers-by to join their Paper Scissors Rock Campaign. It proved an unforgettable experience.
"One trendy, cool-looking guy with a skateboard queued up again and again," says 23-year-old Tsang, of Hong Kong University of Science and Technology.
A shopper prepares to play Paper Scissors Rock in Mong Kok.
"At first, I thought he did that because he'd lost the game. But actually he just wanted to play again." The great response to the event led Li to set up an organisation, Laughfull, to help Hongkongers see the funny side of life.
"Laughfull means 'full of laughter'," says Li, a 24-year-old graduate of Chinese University, who now works as a bank consultant. "Our aim is to bring joy and laughter to Hongkongers by enabling them to take part in creative, happy and meaningful experiences."
His idea was inspired by his visit to Frankfurt, Germany, in 2011.
"I visited a small town where there's a museum with a grassy area outside," says Li. "At the time, some people were protesting against a government redevelopment plan of the area. They protested by inviting everyone in the community to bring their favourite childhood toys and fill the grassland. Their peaceful ways and idea of using toys to show what's important to them made me realise happiness is a simple thing. I asked myself: what can I do to promote happiness?"
Together with Tsang and Wong, a 22-year-old graduate of the University of Hong Kong, Li began to promote a culture of fun in Hong Kong. There are now eight committee members, but anyone sharing the same passion is welcome to join them.
The group members get together regularly and think up ideas for forthcoming events. "We ask ourselves what kind of activities will possibly attract and amuse people, and we think back to our own [childhood] hobbies and interests," says Tsang. "We realise the games we enjoyed the most are those that are relaxing and casual."
Since last year, they have run several fun gigs which, they believe, provided positive energy in the city. Those events included the "High Five Festival" held in co-operation with Lovjoy, a local organisation promoting social engagement and corporate social responsibility. On two mornings, they lined up in the busiest areas of Central and Wan Chai, holding up a set of slogans, and invited pedestrians to give them a high-five. The event attracted 250 participants.
In January, they invited people to write down their wishes in their "This year, I wish ... " activity in Mong Kok.
"We were touched by people's wishes," says Tsang. "Many were writing their wishes for others. Hong Kong isn't dying from want of good wishes yet."
Two Hongkongers add their 'This year, I wish' comments back in January.
To spread the group's message that "everybody can make someone happy", they have run workshops in secondary schools and universities in Hong Kong and Macau.
Last October, Wong represented the group at TEDxCUHK, a forum encouraging creativity held at CUHK.
Taking part was like a dream come true, says Wong.
"I was honoured to spread our mission and ideology. Many people approached us after the talk. My friends from overseas later watched the video of it and were inspired to launch activities, too!" she says.
People define happiness in different ways, and some tie it to material wealth. But to members of Laughfull, happiness does not require the possession of anything; it can mean just spending time with someone you love and care about.
"Happiness is in our blood; we can all bring happiness to our city!" Wong says.