The concept of Sin - anything not of faith that works by Love.
If Getting tattoos were a sin, then God would not save those who have them. Same thing with cigarettes and drinking. After all, there was a time in which Women wearing trousers/pants was considered a sin, because of Deut 22:5. We now know that it means the particular clothes, not the style of the clothes. Moreover, the Law has been abolished. And we see people wearing trousers and getting saved and spoeaking in tongues.
I don't know if any one has been to a non Christ Embassy church in America, but I tell you, sometimes you'll see people dressed all goth - rings, tattoos, painted hair, black lisptick, boots and all. And these ones will pray for people who are sick, and they get healed in Jesus name. They'll speak in tongues, they'll win souls to Christ. So, lets not place a tag, but leave the HolyGhost to deal with each man as he sees fit.
However, Like Big Bros Pauly said: "All things are lawful, but not all things are expedient; all things are lawful, but I will not be brought under the power of any."