June 4 is a political taboo for the Chinese Communist Party. For a quarter of a century, the Beijing authorities have sought to silence the sympathisers of the Tiananmen Square student movement that ended in a bloodbath in the summer of 1989.
In Hong Kong, both the government and pro-establishment figures are usually caught in an embarrassing situation. They do not want to offend their masters in the north; they are equally mindful that anything they say in defence of Beijing on this matter would trigger a public outcry here.
When asked about Tiananmen, all they can muster are non-answers, such as "I have nothing to add". Or, like Chief Executive Leung Chung-ying, they simply walk away, pretending not to hear the question.
They have long accepted that it is better to leave the June 4 protesters alone. Beijing officials seem to have understood, and tolerated, this political peculiarity in Hong Kong.
Over the years, prominent Beijing loyalists such as Lau Nai-keung, Tsang Hin-chi and Maria Tam Wai-chu have ventured some "alternative" views. They argued that Hongkongers should leave behind their "historical baggage". Some blamed the student leaders for failing to end the movement at the right moment, while others urged the public to focus on the country's revival through economic development.
They have, however, never gone as far as asserting that no civilian was killed in Tiananmen Square during the military crackdown. They have never claimed that People's Liberation Army soldiers had been lynched by student mobsters. More importantly, they have never resorted to physical aggression.
The scene has been markedly different this year. It has changed apparently in line with an earlier statement by the head of the Central Policy Unit, Shiu Sin-por, that the government would not sit on its hands when criticised by activists. Of late, small but vocal groups have mushroomed to interfere with the otherwise peaceful forums, rallies, demonstrations and protest marches of the pro-democracy camp. Members of these groups often hurl verbal abuse at the event organisers.
The police, who are supposed to facilitate peaceful protest activities, are often seen as being biased towards the rabble-rousers. Time and again the scene has turned ugly and violent.
The leaders of these groups were virtually unheard of a couple of years ago. Among others, Leticia Lee See-yin of Justice Alliance, Chan Ching-sum of Caring Hong Kong Power and Fu Chun-chung of Defend Hong Kong Campaign have now become newsmakers solely because of the abusive way they take on their opponents.
Under the banner of "Truth of June 4", for instance, a group of provokers set up an exhibition at the Southorn Playground in Wan Chai while a protest march was in progress last Sunday ahead of the 25th anniversary of the bloody suppression of the Tiananmen movement.
Again, police had to intervene. Instead of focusing on the procession, some news media instead magnified the confrontation in the name of "balanced coverage".
Leaders of these disruptive groups are so media savvy that they know exactly how to conduct themselves to steal the limelight.
They have stepped up their efforts to tackle the pro-democracy groups, particularly the organisers of the annual June 4 memorial rally at Victoria Park that has become a focal point of the international press.
They tried to meddle with the opening of the June 4 museum in Tsim Sha Tsui, which was established by the Alliance in Support of Patriotic Democratic Movements in China with a collection of artefacts from victims of the 1989 crackdown. They even targeted the annual June 4 ritual itself. Patrick Ko Tat-bun, convenor of Voice of Loving Hong Kong, set up his own post outside the Tin Hau MTR station to shout at participants of the candlelit vigil in Victoria Park on Wednesday. He showed photos and videos claiming that there had been no killing and that it was the student protesters who had turned violent. He called on Hongkongers to "forgive and forget", accusing the June 4 rally organisers of perpetuating a lie for 25 years.
As many as 180,000 people showed up at the rally this year, a record number. Ko and his small group were obviously out to provoke. Their presence led to a tussle and police officers were mobilised to restore peace.
Since Leung took over as chief executive two years ago, he has adopted a hawkish line against his critics.
The clashes we see on the street now are a natural extension of his "two-line struggles" approach, first advanced by the Red Army in the 1930s. In a nutshell, one is either a friend or an enemy.
Gone are the days when people from across the political spectrum could debate, deride or denounce each other in a peaceful manner.
Albert Cheng King-hon is a political commentator. firstname.lastname@example.org