sadieko started it
When Kakashi had begun to stumble all over the topic of menstruation, Sakura could have killed herself. Or perhaps Naruto, who was looking at her with an undisguised amount of awe. Or even Sasuke, who was turning green at the very thought of her system and looking like he wanted nothing else than to saturate his mind with bleach for a month.
"And the cramps," Kakashi held his chin thoughtfully, as if remembering something from long ago. Rin had been such a PMS bitch. "Sakura will most likely be having those. Teamwork might be suffering later on because of them, even."
Yes, homicide was looking very nice right now.
"Kakashi-sensei," she said, slowly and carefully (no, her teeth were not grinding. Not. At. Fucking. All.), "it's not quite... that
"Of course it is," Naruto shuddered. "You pour blood out of your -"
Sasuke made a gagging noise in the background, but by now Sakura was too angry to pay attention to such petty things.
"Naruto, if you do not shut up this very minute, I swear I'll-"
Naruto's morbid curiosity could not be conquered. "And do you actually stick something up your-"
Kakashi turned away from the delightful conversation to watch Sasuke run for the closest bathroom. Well, there went the rebuilding of the Uchiha clan. Sasuke was apparently disgusted by vaginae.
Like there was any doubt.