harassassin
A.k.a. "assholeassin". A hired exterminator of fellow humans who brings about the demise of his marks by behaving like such an intolerable jerk that the stressed-out unfortunate eventually commits suicide in order to escape said obnoxious persecution.
One should take care how he treats his fellow humans --- like they say, you never know what battles someone else is fighting, and so some people could be "pushed over the edge" by even minor;y-upsetting actions/attitudes on the part of another. Many a cranky schoolteacher, headmaster, stepmother/mother-in-law, etc. has been a literal harassassin, often without even being aware of it at the time.