Are my parents being too harsh?

I want to get a second piercing in both my ears, a cartilage and my nose pierced when I'm 16 and a tattoo when I'm 18 (these are the legal ages I can get these done in my area without parental consent). This came up during a family discussion at dinner and when I told them what I was going to do my dad told me: 'if you dare come back one day with any of those things, especially a tramp stamp (his phrase for a tattoo on the lower middle of the back, which is where I want mine) at any age I will knock you into next week' or words to that effect. When I just laughed he said, 'I'm being serious.' and I could tell from his tone that he was. I asked my parents why they had such an aversion to piercings and tattoos and said that they didn't like them and that they're tacky looking. This is fair enough, everyone is entitled to their opinion and I was respectful of it, but they completely disrespected mine and were very rude to me. It's not their choice to make, and I don't see why they should be allowed to threaten me with violence if I do something that allows me to express my individuality. What can I do about my parents so that I can do the things I want without getting whacked? And are they being too harsh or are they jusitified? Thanks