For me, this is the injection of anesthesia at my latest consultation at the dentist, it was so painful that i screamed to him. Anesthesia is rarely a time of pleasure, but damn, it has never been so painful.
I had a bulging disc and one day I was laying on the couch and sneezed. I felt this pop in my back and the pain was indescribable. I started helplessly crying and yelling for help. After waiting in pain for 20 minutes, my gf brought me to the ER where I cried in the lobby for 8 hours straight waiting to be seen.
Turns out I herniated my disc. I went to PT for 6 months and have slight nerve damage to this day. Funny enough a new latex mattress saved me. I live pain free every day when before that was unthinkable.