I've killed a lot of sims for the Black Widow Challenge and I've gotta say my favorite way to kill sims is either drowning or hysteria. I've tried starving but it takes soooo long omg. But what meth...
Eletrocution. Orignally, I set up a club that was dedicated to building robots for my Sim's science store but turns out the robotics bench is quite deadly for unskilled Sims.