I'm not saying it's regular. Most people into body mods only go so far as tattoos or a couple piercings. That kinda shit's more on the extreme end of things.

Aliens are aliens because they didn't originate from Earth. Uh, our home planet. Humans I'm pretty sure are the only other sentient species, so that makes the not-humans from not-Earth the aliens. They're...extra-terrestrials.