The history of tattoos. Malignant ones vs. benign ones. The most common tattoo in the world is still Mom.
The various styles and kinds of tattoos, and some tattoo rules (#1 never get a name tattoo unless it’s your child. #2 never get a facial tattoo. #3 don’t get a tattoo in Chinese or Kanji unless you can actually READ Chinese or Kanji. Otherwise you risk getting the Chinese ideogram for “dumbass” tattooed on your skin.