Your friends are too quick to judge. You can assure them that you are not going to get aids by informing them that aids is only transmitted through blood transfusion and unprotected sexual intercourse, and you can also assure them by saying that there will be no sexual intercourse and you'll be cautious in not having his blood transfused into you.
I would say the teen doesn't think of the consequences that not having good health habits maybe affect them in their life later on. Also maybe the parents don't encourage them to live a healthier life.