A person or device that turns something upside down(noun)
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Use "upsetter" in a sentence
"Did anyone ever notice that in the last 100 years the only time the Democrats could win the presidency was if there was a third pary upsetter 1912, 1992"
"KING: Every time I moderate a debate on this issue they get upsetter and upsetter."
"KING: Every time I moderate a debate on this issue, they get upsetter and upsetter."