Butthurt is from spanking. I guess some folks retconned it otherwise, but its origins are from spanking. http://knowyourmeme.com/memes/butthurt

I guess it comes from how spanking hurts but not actually all that much & fades quickly, but kids usually cry and scream disproportionately about it. But on this part I could just be conjecturing. I got spanked as a child until I faked being more upset than I really was about it then my parents stopped the practice.