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Ways to kill someone with kindness:
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Keep vacuuming the apartment - until there's no oxygen left in it!
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Make sure the poison is extra yummy.
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Build giant concrete art installation of the word "kindness", wait until the right moment to tip it over.
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Give them puppy-dog eyes and ask
pretty please if you can decapitate them.
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One too many soft pillows...
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Live with someone for five years without ever doing a single household chore and then suddenly clean the entire apartment really well and watch them die of a heart attack.
LOL.