If you're going to get a tattoo, you should go to a clean, reputable tattoo shop. Getting ink in an airplane...not a good idea!
Watch this video of a guy who is tattooing another man's hand during a flight. Right there, palm on the folding tray, with the needle going. Definitely NOT sanitary. And what if there was turbulence?! Oh, sorry about that extra line halfway up your arm. Whoops.
What are you boneheads thinking?!