House plants can be a chore for some people to take care of. Remembering to feed and water them is just not their thing. Or they just don't have a knack for gardening. Other people might know how to take care of plants, but have a plant that has never done well. The plant looks scraggly but won't die. Whatever your relationship with plants, or if you have your own reasons for killing a house plant, there are a few obvious ways to kill it and a few that require some supplies.
Pull the plant up by its roots and add it to a compost pile There is no need to waste the nutrients that are inside.
Stop feeding and watering the plant. Put it in a dark area to deprive it of light. It will die slowly, but it will go eventually.
Spray the plant with a mixture of water and vinegar. The strong acid in the vinegar will kill almost anything.
Add salt to the acid mixture if the plant is still alive. Salt will render the soil uninhabitable and kill anything trying to grow in it. If you plan to grow something in the soil after the plant is dead, you can add baking soda and water to the soil to bring it back to a proper growing medium.