People who for some reason love to create meaningless drama for others. This involves arguing about some issue that no one really cares about, or attacking someone personally for some minor wrong things that they do or some non-issue. Becomes even worse when the victim won't stand up for themselves.
People who do this shit are pretty low individuals and are the type of people that you see on the Jerry Springer show, have drug or alcohol problems, worship the tabloids, or are a commentator/"journalist" on Fox News.
A good example of starting shit is in Back to the Future.
Biff: I can't belive you'd loan me your car...without telling me it had a blind spot. I could have been killed.
George: Now, now biff, now, I never noticed that...the car had any blind spot before when I would drive it. Hi son.
Biff: What are you blind Mcfly. It's there. How else do you explain that wreck out there.
George: Now biff, um, can I, can I *assume* that your insurance is going to pay for the damage.
Biff: My insurance? It's your car, your insurace should pay for it. I wanna know who's gonna pay for this....I spilled beer all over when that car smashed into me. Who's gonna pay my cleaning bill? And where's my reports?
George: Uh, well, I haven't finished those up yet. But ya know, I figured since they weren't due till' Monday.
Biff: Hello, anybody home, think Mcfly...think. I gotta have time to get them retyped. Do you realize what would happen if I turned in my reports in your handwriting? I'd get fired. You wouldn't want that to happen would ya'? Would ya'?
George: No Biff, of course not Biff, I wouldn't want that to happen. I'll finish those up tonight, and run em' on over first thing tomorrow all right.
Biff: Not too early, I sleep in Saturday. Hey Mcfly your shoes untied. Don't be so gullible Mcfly. You got the place fixed up nice though Mcfly. I have your car towed all the way to your house, and all you got for me is light beer? What are you looking at Butthead? Say hi to your mom for me.
George: I know what your gonna say son. And your right, your right. But Biff just happens to be my supervisor and I'm afraid i'm just not very good at confrontations.
one of the many uses of the word shit, in this particular case it means someone is creating drama or wanting to fight.