I just shift click and select kill... usually by spell caster overload or wild bunnies. I guess it depends on how much storyline you want with it. My story line is that certain sims are cursed and die of the overload. It's quick and easy.
If they are an active member of the household then make sure to shift click on the Sim who's active or you'll kill another sim on accident. If they aren't active in the household (townie) you just shift click on the townie and it kills them even though your Sim is active.
Play as Clement, shift click on Clement and select your kill method if he's active. If not just shift click. That said if you kill clement you'll spawn a new Father Winter.
