One rule I've always used, for anything that would be remotely permanent, is meaning. Does it have meaning?
Tattoos have never been a personal favorite. But, for example with US Marines, it is pretty much a given that they will have the anchor, or Chesty tattooed on their forearm. And, I don't begrudge them that. It is a meaningful symbol, and one which will stir memories throughout their lives.
It's also a classic symbol, and that's important for something that will be as permanent as a tattoo. The current fascination with tribal art, or tramp stamps may not be so "fascinating" in 50 years. But your tattoo will still be there, even if you're a Grandpa!
I am trying to lose a significant amount of weight, and nearly 12" in my waist. When finished, I am sincerely considering rewarding myself with a *genuine* Maori moko...in fact, it's already been approved by one of their tribal leaders. Moko are a specific tribal tattoo, ideographic in nature, that tell a story, and which are unique to the wearer.
Definitely meaningful.