Not a pastie, it's clearly a common (you old farts in small cities won't know, lol) nipple ring with a circular retainer. I see them all the time on young girls here. If you watch in in slow motion like I did, you can clearly see the look in horror on her face, and a piece of red in Justin's hand. I view it as an accident, her red bra was probably very thin material, and Justin grabbed underneth instead of over it and ripped it off.
While I'm on the subject, lemme just say I don't find anything wrong at all with it being on live TV, and I'm a hard-line conservative. C'mon, it's just a nipple that was on TV for like 3 seconds at best. Only in America would this be a big deal.