A millennia ago there was a highly skilled monk that travelled the lands. While his name has been lost to the ages, he was commonly called Snu-Snu. An extreme celibate, Snu-Snu was disgusted by any form of sexual arousal outside of intentional procreation, and that even that was to not result in any pleasure to be had. He also claimed that his martial powers came from his celibacy, and that not even the Gods could tempt him.
Well, the Gods are a fickle and egotistical bunch. A majority of them got together to decide how to punish Snu-Snu for this effrontery. The debate quickly turned into a shoving match, and tempers flared until Sinela, Goddess of Humor, Lust and Chaos, offered a punishment idea that turned the fisticuffs into roars of laughter. The punishment was the most dramatically ironic punishment that had ever been inflicted upon a mortal before or since.
Soon thereafter, Snu-Snu entered a martial tournament that was known throughout the realms as one that would prove who the greatest martial artist around was. Snu-Snu won his first two combats quickly, pummeling his opponents into unconsciousness with a few powerful hits. His third combat was rather different, however. When his first punch landed, his opponent moaned and became obviously turgid under his robe. As punches contacted, Snu-Snu's foe moaned louder and louder and quickly became distracted. One last blow from the now furious monk caused his opponent to orgasm loudly and messily, falling unconscious and spent to the floor.
The laughter of the crowd caused Snu-Snu to become quite red. How could his enemy be so disgusting, to receive sexual pleasure from the pain that was being inflicted? He demanded a new opponent, and one was supplied for him. A woman this time, the exact same thing happened yet once again except that a fairly large puddle of vaginal lubricant and piss was left on the floor as well. This was beyond vile! How could such a thing happen? Disgusting! And why are they all laughing? The entire crowd is filled with perverts!
It soon became known that Snu-Snu could do nothing but inflict loathsome and nauseating sexual pleasure upon any living creature that he fought against, much to his ongoing chagrin. No matter where he went his reputation travelled with him, and while Snu-Snu was largely forgotten his name eventually became a term for the sex act. The term "Death by Snu-Snu" was coined by an all female barbarian tribe due to their preferred method of executing males.
Sinela didn't forget, however. Once in a generation a monk is inflicted with the Curse of Snu-Snu, simply as a joke on Her part. How this curse works is as follows: The monk is completely unable to inflict lethal damage with his unarmed attacks. Every attack causes his foe to become more and more sexually aroused, resulting in a -1 To Hit for every 10 HP of damage the monk inflicts. Once the enemy is at 1/2 HP, he or she has a strong orgasm that leaves them STAGGERED for 1d4 rounds. If damage exactly equals his current HP he is STUNNED, and if his nonlethal damage exceeds his HP he has a massive orgasm and becomes UNCONSCIOUS. This happens with any humanoid or non-humanoid creature that is capable of having an orgasm (undead are immune for obvious reasons).
The curse can only be lifted by having a Remove Curse cast upon the sufferer by a Lv 20+ spellcaster, or with the use of an Alter Reality or full Wish spell. Sinela will occasionally take pity on the poor monk, but this has been known to have happened only twice in the past thousand years. The curse itself is considered to be a Flaw, as described in the 3.5 Unearthed Arcana rulebook. It does not grant a bonus feat, however.
