Does apple cidar vinegar kill bad bacteria in the vagina?

No. Don't ever douche or squirt anything non-prescription into your vagina (except otc antifungal creams); doing so can cause infections. If you have a vaginal infection, it needs to be treated properly.
Unnecessary. Douching is totally unnecessary and in fact contraindicated. You do not want to change the bacteria in the vagina without a good reason to do so. If you have bacterial vaginosis there are antibiotics that your ob/gyn will treat you with. Do not use apple cidar vinegar.