I want to know why it's a bad idea pure white vinegar applied inside the vagina.

See answer: Vinegar douche has been used to treat Candida yeast infections, by restoring the normal acidic vaginal pH. However, douching has many undesirable consequences and unlikely to cure yeast vaginitis. Women who douche have more bacterial vaginal infections, a higher incidence of PID, more difficulty getting pregnant. SEE > http://wb.md/1RIByhY and http://wb.md/1jTeuzk