Okay I'm open minded and would be fine if he got a small tattoo somewhere but he wants to get both his arms fully inked and all of his upper back too. Its not even something meaningful, just a bunch of skulls and guns. I love him and its his body but don't you think he's crossing the line. When my parents see him I know there gonna hate him even though hes a nice guy because of his tats. Or when we go in public people are gonna judge us and think he's a bad person.

How do I stop him from getting the tattoos?

P.S: I told him to get smaller ones but he has this entire design planed out for months and he's really upset now.

BTW: Were both 22

First off lets think for a second here.
Do you really think the relationship is destined for the "long" run?

No offense but if you really disagree with this act that hes taking upon himself then are you guys really made for each other? The typical bad boy look is hot but only for so long. A man that wants to get full set sleeves is not looking into a professional career, unless he wants to be a rockstar, tattoo artist, or just plain old famous.
If he has his mind set on this decision than there is nothing you can do but
A. Support him
B. Reconsider the relationship or
C. "F" it for now hes fun loving and we'll see where it goes.

Your 22, do what you want but make sure you consider yourself in the equation!