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1. human petri dish
a person who is always sick and spreads their germs where ever they are.
Alan is such a human petri dish. He always has a cold and sneezes all over the place.
2. Human Petri Dish
A. someone who continuously sticks needles into their skin: medically and heroinically.

B. someone who allows experiments on themselves.
"That guy must be a human petri dish, son of a bitch has moss growing on his face."
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