"I'm a heckler!" (3)

I believe the answer is:

boo

(Other definitions for boo that I've seen before include "Frightening word (for a goose?)" , "Sound made to show disapproval or contempt" , "Show displeasure orally" , "Disapproving sound" , "Express noisy disapproval" .)

I've seen this clue in the USA Today.

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