gadfly

IPA: gˈædfɫaɪ

Any dipterous (“two-winged”) insect or fly of the family Oestridae (commonly known as a botfly) or Tabanidae (horsefly), noted for irritating animals by buzzing about them, and biting them to suck their blood; a gadbee.
(figuratively, also attributively)
A person or thing that irritates or instigates.
(specifically) A person who upsets the status quo by posing novel or upsetting questions, or attempts to stimulate innovation by being an irritant.
Synonym of gadabout (“a person who restlessly moves from place to place, seeking amusement or the companionship of others”)
(derogatory, slang) A person who takes without giving back; a bloodsucker.

Examples of "gadfly" in Sentences

Q: You've been called a gadfly, a consumer activist.
Being a gadfly is certainly a role, and occasionally a helpful one.
And sometimes the gadfly is off base and really doesn't understand what is going on.
History shows that once in a while even a so-called gadfly has been able to effect change.
The Alaskan resident – now being referred to as a gadfly – criticized where she felt it was due and gave credit where it appeared there should be some.
Boris Pincus, a former Queens resident who serves as Republican District Leader of Assembly District 45 in Brooklyn, has long been known as a gadfly within the Bukharian community who is biting in his criticism of the communal leadership.