It's rude, okay? This is my life, and my face, and I'll do whatever the heck I want with it. I'll be 23 years old in two days, I think I'm old enough to start making my own decisions here, mmkay? I understand that it's not your thing, but it is mine. When you say it's disgusting, you're calling me disgusting. Which, fine, but would you say to my face "Wow, you're disgusting!"? No? Well, then don't say it about my piercings. It's the same thing.
And I'm insecure enough as it is. When you say things like that, it hurts. Really.
But I'm not going to change my mind just because you think I'm stupid. If it bothers you that much, just stay away from me. I'm not forcing you to spend time with me. I'm not forcing you to be my friend. But if you want to be? You know that saying "If you've got nothing nice to say, don't say anything at all"? Do that.