They have weird eating habits
There are questionable food habits that imply that you're capable of murder. Do they eat their pizza with a fork and knife? Do they eat a candy bar with a fork and knife? Do they eat their steak well done or with ketchup? Do they eat Oreos by biting directly into them instead of pulling them apart? Do they eat food on the subway? Do they drizzle their food in ketchup instead of putting it on the side? Do they eat lobster rolls from McDonalds? Do they microwave sushi? If the answer is yes to any of these, they're a sociopath. After all, you are what you eat, and these freaky eating habits make you a freak of nature.
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