This term is not a usual Spanish slang. It seems to be a literal combination of two words 'postre' meaning dessert and 'vigilante' meaning guard or watchman. It does not have a specific slang meaning in Spanish.
Examples
- Spanish: No hay un ejemplo válido ya que 'postre vigilante' no es una expresión comúnmente utilizada en el español coloquial.
- English: There is no valid example as 'postre vigilante' is not a commonly used expression in colloquial Spanish.