Only if you can bear out with evidence an assumption you have about these people as a group. Then you're free to extrapolate your dislike of the thing they have in common which piercings are an indicator of to the people themselves. Meaning, if these people tend to have a certain behavioral trait in common then the piercing may be an indicator of that trait, and if this is a trait you hate, you're probably not going to like people patterning with it.

However, if you aren't certain of at least that much, then the group of people you're disliking is arbitrary and without basis. I dislike piercings of any kind, including earrings to be honest - but I can find no quality or vice pierced people have in common to either like or hate the people rather than the style. For me, they do not form a coherent group beyond the superficial fact that they all have piercings.