Worst I can remember is when I went ice skating with my dad when I was 9yrs old. I was running my hand along the glass of the rink while skating when my pinky finger got caught between two panes of glass, and I twisted the bone out of place. I just stood there for a moment, holding my finger, thinking about how much that hurt. Then went back to skating like nothing ever happened, never told anyone till years later, the bone is still funky.
Another time was when I was much younger... maybe 6yrs old? Me and my mom were at a dealership, and I was walking along a square railing outside, totally unsupervised. My foot slipped and I gouged the side of my face on the corner of the railing, leaving a huge gash in my cheek. If I remember right I didn't even notice it at first? I just thought that I bumped my face a bit, it sorta hurt, but then I walked into the dealership to see mom. The next thing I know she started freaking out cuz I was bleeding everywhere. Upon hearing this I barely reacted, it probably didn't even register for some reason.
Being someone who grew up with chronic migraines, and still has them, I have a pretty high pain tolerance. Growing up with cats, and regularly getting scratched and bitten also helped.