Genital warts
In rare cases, genital warts can use the wound from a piercing to "flower" from. Genital warts (HPV) affect between 1 in 10 and 1 in 5 people in the United States. It is the most likely STD for you to come in contact with, and many people who suffer from it are unaware of that fact. (That is, you or your partner may already have it).
It is not unusual for genital warts to "grow out of" fresh piercings and genital cuttings. In addition, if your fresh piercing or cutting comes in contact with warty tissue it can almost immediately sprout warts of its own. Because genital warts are caused by skin-to-skin contact with the Human Papilloma Virus, they can be transmitted to different body parts, and between partners.
For example, if you get your tongue pierced and then give oral sex to someone with genital warts, you could soon after have giant warts flowering out of the top and bottom of the piercing. Alternately, if you have genital warts (and like I said, you may not know it) and get a genital piercing, it is possible for the warts that you didn't know you had to suddenly flower out of that piercing hole.
While genital warts do often just go away on their own, that is usually less common in these cases. You should DEFINITELY see a doctor if this happens to you.
For females in particular, certain forms of HPV can lead to precancerous chances in the tissues of cervix. A Pap smear is currently the only available test for HPV (and is only for females). If yourself or a female partner observes genital warts or has abnormal Pap results, please see your physician for additional follow-up.