Yeah seriously. Lead, Arsenic, and all sorts of other interesting items from the periodic table.
These normally work too fast. One would want to have something slow acting there.
Force feed him plenty of pork chops , pork roll, bacon, ham, pork ribs, pigs feet, pork rinds, biscuits cooked in pork fat, Noodles in vodka sauce, veggies in wine sauce till he's too fat to hang or explodes.