If a girl does or offers this sort of thing it's either they're ignorant of what they can catch or pass on or maybe they offer BB on the quiet , the first girl I had a punt with did this to me and presumably other punters as well (Sexy_Sarah, Bolton no longer punting I might add), this was some years ago and none of the test have come back positive. I've read that it is possible to pass on the HIV virus by doing this sort of thing through an infected womens vaginal fluid. So maybe you might want to think twice about doing it.