it remain overnight in the water solution. you can wash it after that.
if vinegar is not easily available, then you can use club soda which is equally effective to remove coffee stains. you can pour some quantity of club soda on to the stain and continuously rub until the stain disappears.
if you can lay your hands on baking soda, then your worries are put to bed! take a cold, damp handkerchief or towel and wet your shirt. sprinkle small quantities of baking soda all over the stains. let is slowly seep. gently rub using a dry cloth. although, this will not remove the coffee stain permanently, it will nevertheless soften 