Personally, I ask them if they would do bbfs so that I know who to stay AWAY from. I hope that's what others are doing too, and not tring to spread their aids and herpes.
Good plan, but it might just shoot you in the foot... lol
I don't know about other girls, but the question of bbfs has VERY RARELY come up in my experience, and each time it has... That person quickly found himself blocked and on my Blacklist!