Heat oil in small saucepan over high heat and stir-fry curry paste 15 seconds. Stir in coconut milk and bring to boil; boil 2 minutes. Add peanut butter. Stir constantly until sauce begins to thicken, 2 to 3 minutes. Reduce heat to simmer and add fish sauce, rice vinegar and sugar. Cook sauce, stirring, 1 minute more. Remove from heat. An oily film will rise to top; skim it off if you wish.