The absolute strongest curse word ever created in the English language. It is so strong the lightest situation it can be used in is something on the same level as the scenario that follows:
You come home and see a man there with a bloody axe and the bodies of your fallen family ---- He runs and you give chase, you catch him and pry the hatchet from his hands, and while you hack away at his face, hoping to cause as much pain possible you're yelling one word the whole time.
The murder of only 1 family member wouldn't quite be strong enough to warrant the usage of the S-Word
"Hey man, someone murdered my sister yesterday...I was just walking around the park yelling the S-word (Stash)"
"wow you were way outta line man, you should post a formal apology in the park"