Place rib tips in a large pot and cover with water. Place over high heat and bring to a boil, cook for 10 minutes then strain.
Make the sauce by mixing pineapple juice, ketchup, soy sauce, brown sugar, red pepper flakes, crushed garlic and salt in a small bowl and set aside.
In a frying pan wide enough to hold the ribs in one layer, place 1 teaspoon oil and heat over medium fire.
Add ribs in a single layer and cook for about 2-3 minutes on both sides allowing it to brown. Once the ribs have browned on both sides, use a spoon to carefully remove excess oil.
Pour the prepared sauce over the ribs. Cover the pot and cook over low heat and allow ribs to simmer in the sauce for 30 minutes while stirring occasionally.
After 30 minutes the sauce should have reduced and begin to cling to the meat.
In a small bowl mix cornstarch with cold water, then pour over ribs then stir. Cook for an additional 5 minutes on the sauce thickens.
Remove from heat and garnish with chopped scallion.