I use to be a piercer and i got mine done i think it has to be one of the most painfull things ever. Most of the men that got their nipples pierced screemed, im not kidding for men its even more painfull. So make sure you really want it hurts like hell. But it feels fine in like a week.
I'm a guy who has got mine done, both of them several years ago. Yes, of course it hurt, but it's definitely worth it. They're pierced vertically with barbells. I have no regrets and would like to see pierced nipples on a lot more guys. You pay a lot more attention to your nipples and you'll find this a rewarding thing. Good luck!