I have a thick beard and long hair I wear in a ponytail. I've had people tell me I'm the kind of person they "expect" to see armed. I'm not quite sure how that works, but it seems to be true. I haven't been questioned about being armed in years (beyond the occasional, "do you need a permit?").
If you really want to be ignored, I've learned that the biggest "sell" is your ability to walk into a room or down a street like you own the place – as though you know exactly what you're doing, you're exactly where you belong, and nothing is up for discussion.
That said, I do think piercings on a male will make it harder to be taken seriously. Even at this advanced date, they seem rather childish (and no, this is not coming from a middle-aged person).
I would never suggest that piercings are an impediment to normal, everyday OC. But I do think they're going to be a greater impediment than some hairstyles, and most well-groomed facial hair, if you wish to pursue to "act like you own the place" approach – which is itself by no means a requisite to successful OC.