First make the sauce. Use a fork to scrape the plum flesh from the stone. Heat the vinegar and add the sugar and plum flesh, stirring until the sugar dissolves which will take about 2 Minutes. Simmer until a thin syrup begins to form, then remove from the heat. Stir in the chillies, pour into a bowl and set aside.
In a mixing bowl, stir together the crab, coconut, egg, garlic, sauces and pepper. Knead with your fingers, then form into small patties. Roll in the breadcrumbs until well coated.
Heat a pan of oil to 200°C. Deep-fry the patties until golden brown. Drain on kitchen paper and serve with the plum sauce.