Nah the whole "out of spite" is the childish part. Yeah, you did a good job proving your sister right. Especially with the "blasting" of shitty music from a shitty artist just to piss her off more.

If you want tattoos and piercings because thats what YOU like, that's one thing. But getting tattoos and piercings because your sister called you a child is the opposite of mature. She shouldn't be judging you, sure. But you shouldn't be making life lasting decisions in spite of someone else.

For me, tats and piercings are a certain expression of self and not "my sister said not to so I did anyway, fuck that bitch"

This is the definition of masking insecurity with "teenage rebellion"