My friend in high school went to go get a tattoo to celebrate graduating, and she got the first line drawn. Couldn't handle the pain very well and also had doubts about getting one at all.
So now she has what looks like a hair on her shoulder blade.
Didn't chicken out, but aged 13 we dared each other to give ourselves tattoos. I went with a cross on my calf. Ran out of ink most of the way through, so, over 30 years later, still have T on my calf.
My tattoo artist told me a story about how he was doing a pretty large piece on one of his clients, and the guy fell asleep about 1/3 of the way in.
When the guy woke up, he freaked out and had no recollection of what was happening - he stopped the tattoo right there, and from what I hear, it's never been finished.