Actually the nipple rings are used to bypass airport security thanks
to incompetency of TSA

Before the evening flight on Airbus flight 911 with 853 seats, the
woman and her companion removed her large 44D saline implants and
packed the space with C-4 plastic explosives and detonators. To get
through security, she installed gold plated steel nipple rings that
were sure to set off the devices controlling access to the TSA
monitored security area.

Buzzer alarms went off when she walked through security The hand held
wand device was used to detect the metal in her chest area. She
explained that the nipple rings were the source of the problem and
that they were not possible to be removed. The female TSA employee
requested she step into the nearby curtained area and reveal the rings
for verification. Upon verification she was allowed to leave
security and boarded her flight to New York's largest airport. The
boarding ticket showed her seat to be 535D, which was directly over
the mid ship fuel tank.

Once the seat belt light went out she layed down on her stomach in the
small area in front of her seat and pressed the ignition button
implanted in her left breast.

853 souls perished at 32,000 feet.