How to convince parents to let me get a tattoo, i am 18!?

i know i know this is prob going to get negative response but i believe going behind your mom and dad back is never a good idea. They prob have there reasons and prob have good reasons too. maybe one time site down with them and just ask them why they are against it do not say any thing to defend your self cause this is just you wanting to know why they have such a thing against tattoos. then say okay and respect them and not have another argument about tats with them for a Worthyn they might see and feel respected by your responsece and then give there blessing ( its a mom and dad thing to do that). but just kinda go off of what they said cause they have been around longer then us and have seen things and if there any thing like my parents they have much wisdom. i know it is not easy at all cause it feels like they are so old fashioned and have no idea what your are going through. i know i am 17. but they often have much good wisdom.