This disorder is associated with several vascular, neurological, and skeletal problems including stroke, heart attack, clotting, mental retardation, eye abnormalities, and osteoporosis, amongst many other complications.
Tattoo tipping etiquette, in general, should hover around 15% for small tattoos and 20% for larger tattoos, but as with all tips, you as a customer ultimately determine the amount based on the quality of service and the work performed. Consider your involvement as well.
I usually tip $10 for anything under $100 -- piercing and stretching. I think I may have tipped $20 for a branding and for a scarification. Those were a year apart.I'm not totally insane. tipped $5 for both of mine, but it was a shop that let you bring your own jewelry in (they sterilized it for you before they did the piercing) so it only cost $20 each time.