Well, I only headbutted somebody once (in self-defense), when I was still going to school, but I remember that while my opponent seemed to be in pain I myself didn’t feel much of it. Why is that?
I’m not sure in your specific case, but in a correctly executed headbutt it is not the same part of the head that is the collision point on both people. If you just literally “butt heads” all bets are off.
IIRC, the headbutter strikes with the top of the forehead where the skull is quite thick. She strikes down hitting the bridge of the nose of the headbuttee thus breaking the nose and/or making the person pass out with the sudden acceleration of the brain.
Adrenaline is also a surprisingly effective temporary pain killer. Assuming the headbutt was done in the heat of a fight at least some of the pain would be diminished, combined with proper execution and technique the “headbutter” would come out relatively unfazed.
All this being said, a headbutt is a really dumb thing to do. A broken fist has virtually no chance of causing you seizures twenty years later. (But, should conditions allow, the temple, just above and in front of the ear, is a pretty sweet target, too. That’ll ring their bell.)
Nobody wins with a headbutt.
Like trying to crack an egg with another egg.
You got lucky. It normally hurts for both parties.
In addition, the idea of pain is some times more painful than an injury itself, which is why little kids, ladies and sissy boys cry about it.
In all seriousness, experience and familiarity can mitigate a certain amount of pain, as does adrenaline.
TL;DR you can learn to process pain differently.
Ah the headbutt. A favorite topic of mine, for obscure reasons. There are a few parts to this question I think. This also mostly applies to fairly hard hits. For lesser impacts a lot of the psychological factors people have mentioned are the primary factor I suspect.
A headbutt can certainly hurt the headbutter, sometimes more than the headbuttee. Splitting the brow over the supraorbital ridge isn’t uncommon, mashing your forehead into someone’s teeth isn’t a great idea, it can easily lead to a concussion or worse for either party, etc. But that leads to the next couple points.
Ideally you aren’t just clonking heads like two soccer players going for a ball in the air. You are trying to hit his face with your head. The face is soft, crunchy, bleeds easily with blunt trauma, and hurts a lot. Your head is hard, strong, relatively insensitive, and usually only bleeds if it gets cut. In an ideal shot, you land a square, resulting in purely linear acceleration, which is relatively benign. If your opponents head gets spun even slightly, it results in shear forces which are lot worse for their brain.
Perhaps most importantly, in a good headbutt you aren’t hitting someone with your head, you’re hitting them with your whole body, with your head as the point of impact. Your legs and torso (and arms if you are lucky) are generating force and your neck and shoulders stabilize your head so the impact is distributed. If the victim is unprepared, all the force is concentrated in their head.
I would argue, however, that if you are on either end of a headbutt, you’ve almost certainly made some poor decisions to lead you to that point.
SDAB Gfactor is somewhat partial to the subject, too:
Is head-butting for real?
Put intitle:head but site:straightdope.com into Google and you’ll get other SDMB threads.
[Brian Dennehy] “Top of the head…hardest part of the body”
While you may get away with not getting hurt, IMHO headbutts are akin to a suckerpunch.
I headbutted a guy in the chest during a fight many years ago. That was remarkably effective.