My mother did a DIY piercing when she was really younger. Grandma wouldn't let her get her ears pierced, and back then they had these things that had you squeeze at them to slowly pierce one's ears. Mom did that, except without the slowly part.
Another friend did a DIY piercing on her lip as well. She had it done at school, and either her friend used a safety pin or the friend used an earring to get the job done. Within the week her lip was swollen and puffy. Internally I was chuckling.
It frustrates me too when people don't listen. If I tell you 'Dude, that essay is ridiculously plagiarized, trust me, I saw my brother WRITE that essay, you might want to reconsider turning it in.' and then you say 'No way, man. Look, I changed this whole paragraph right here.' and then turn the damned thing in and get EXPELLED for plagiarism... well, it's hard NOT to say 'I told you so', you know?