Asia watchers are used to watching neighbours Singapore and Malaysia lightheartedly lob insults at each other over the provenance of their joint cuisine. But the Southeast Asian countries ended 2018 with a far more sombre dispute than their decades-old food fight - one that has continued into the new year.
The row over airspace and maritime boundaries has given rise to jingoism on both sides, and observers say the bilateral relationship is currently at its worst state in two decades.
The downturn comes after veteran politician Mahathir Mohamad, 93, returned as prime minister last May after an election in which his scandal-haunted predecessor and one-time protege Najib Razak was roundly trounced. Just last January, ahead of the polls, Najib had declared that the "confrontational diplomacy" between the neighbours that marked Mahathir's first stint in power from 1981 to 2003 was firmly in the past. He spoke too soon.
This Week in Asia takes you over the main sticking points in the relationship between the neighbours.
As one of the world's busiest maritime hubs, Singapore is expectedly finicky about its maritime boundaries - especially when they are challenged.
For the Port of Singapore to continue to thrive, waters within the port limits need to be clearly defined and not subject to territorial disputes.
But this was exactly what happened on October 25 last year. Malaysia, through a government proclamation called a gazette, declared that it was extending the boundary of its Johor Bahru port into waters Singapore deemed its own.
The Lion City claims the disputed waters are outside Malaysia's most extensive maritime boundaries - which the island nation also rejects.
Instead, Singapore says "since at least 1999" it has been exercising its jurisdiction in the waters Malaysia claims now as within the Johor Bahru port limit. In a response to the Malaysian declaration, Singapore on December 6 declared the disputed waters to be part of its port limits.
It also filed a declaration under the United Nations Convention of the Law of the Sea (Unclos) that bars any party from unilaterally initiating arbitration or adjudication on the dispute.
Unclos defines how coastal states can establish sovereignty over territorial seas.
The "Article 298" declaration made by Singapore allows countries to trigger an opt-out from compulsory arbitration and adjudication. It is made when a concerned party prefers to deal with a dispute bilaterally. China, involved in the South China Sea dispute, triggered a similar declaration in 2006.
Singapore's declaration means it and Malaysia must agree to jointly seek third-party recourse before any further action can be taken.
Malaysia has said there is absolutely no basis for Singapore's assertions about the waters as the new port limits declared in October "are within Malaysia's territorial sea".
WHAT HAPPENS NEXT?
Malaysia's Foreign Minister Saifuddin Abdullah and his Singaporean counterpart Vivian Balakrishnan in a January 8 statement said they had instructed senior officials to study the dispute and provide "a basis for further discussions and negotiations", with a two-month deadline.
Media reports have said Malaysian government vessels remain within the disputed waters after the foreign ministers' meeting. Singaporean coastguard vessels continue to patrol the waters.
The air dispute centres on Singaporean air traffic controllers' stewardship of a portion of air space in the southern Malaysian state of Johor. Singapore has managed that air space since 1974.
On December 4, Malaysia's Transport Minister Anthony Loke revealed the Malaysian government was unhappy with Singapore's decision to begin broadcasting an Instrument Landing System (ILS), at its secondary civilian airport, Seletar.
The ILS would require planes landing at Seletar Airport to make their approach over Johor - inconveniencing residents and jeopardising a seaport there. Malaysia's position was that Singapore had used its stewardship of Malaysian air space in Johor to unilaterally implement the ILS from January.
Singapore vehemently denied this, and released correspondence showing it had repeatedly made its intentions known to its larger neighbour - both before and after Malaysia's May 9 election.
The city state also disputed Malaysia's assertions about the negative impact of the ILS, stating instead that the procedure merely codified existing flight paths.
Malaysia in the meantime said it wanted to retake control of the air space in a four-year window beginning this year.
Caught in the middle of this technical row over radar systems and air boundaries was the Malaysian airline Firefly, which had agreed to move its operations from Singapore's main Changi Airport to Seletar. The move was part of Singapore's plan to relocate all turboprop flights to Seletar.
However in the midst of the government-to-government dispute, Malaysian civil aviation authorities did not sanction the move.
Firefly meanwhile lost its slots in Changi Airport. It previously had offered 20 daily flights from Changi to various Malaysian destinations.
Malaysia meanwhile declared the air space Singapore had been administering - which was crucial for the operation of the ILS - a restricted military training area.
This move made the operation of the ILS untenable.
WHAT HAPPENS NEXT?
Following the meeting between Balakrishnan and Saifuddin on January 8, the two sides agreed to two things: Malaysia would suspend the restricted status of the affected air space for a period of one month, while Singapore would suspend the implementation of the ILS, also for a month. Transport Minister Anthony Loke and Khaw Boon Wan are slated to meet soon to discuss the way forward in this particular dispute.
Local media reports this week said Firefly was losing 20 million ringgit (S$6.6 million) a week because of the suspension of operations out of Seletar
This article was first published in South China Morning Post.