Not the most painful thing I've felt but when I was about 9/10 on holiday in Orlando I walked into a teenager, maybe 14, at a theme park and his teeth went into my head. Cut my head open badly which didn't really hurt that much but he lost about 5/6 teeth and a couple of them broke as well. Luckily he still had a lot of his baby teeth as apparently only 1 of the broken ones and one lost tooth was an adult one. Did lose a lot of blood though, apparently my entire face and half my chest was covered with blood. All I remember was not being able to see out of my left eye due to blood as I walked over to my mum to tell her I had bumped into someone then she shoved a towel against my head and took me to a first aid station.