Impaled myself on my bicycle handlebars when I was 15. It went in about 2" below and to the left of my belly button. I lucked up and it pretty much pushed my organs out of the way. I was on BLM land in Wyoming alone at the time. I had to pull myself off of the bike and I walked to the nearest house, which was a good 3 miles away. That one sucked for sure, but I was in shock the whole time and didn't really feel too much pain. I just took my shirt off and held my innards in with it and I was all set. The worst part of the whole ordeal was having to have them pack the healing wound with gauze for weeks. Gave me a nice scar too.
For pain... Kidney stones take the cake, hands down. Those are a whole new animal right there. I've passed them twice. I really don't care to do it again.