Why do people laugh at me?

Whenever or wherever I go out, I often get laughed at. I'm almost sure it's because I got my lip pierced (medusa) and many people laugh, stare and say awkward things about me. I always act like I don't care or don;t hear them but it doesn't seem to work. I also remeber being laughed at before I got my piercing so it doesn;t seem to be the only reson. I'm generally a shy person and I'm not self-confident at all and I know this may be a reason, but how can people know it if I haven't even seen them or talk to them before? It really makes me upset sometimes. Like today, I was going back come by a bus and a group of guys were looking at me and saying ridiculous things, swearing and laughing at me. They even came closer to see me better and laughed more. I really don;t understand this. I know piercing is not a very common thing, especially medusa, but come on. Do people have to be so sassy? I'm adding a pic so you can see me. I don;t consider myself that uglybut because of situations like this I feel very uncomfortable with myself.. http://i52.tinypic.com/5ujoy9.jpg this is me.