It means eventually being an asshole gets you in the shit yourself maybe.
Karma is an ahrimanic bond that can either help/hinder your life/fate/destiny all in relation to your actions/choices that you make in your life. If you are cruel to people in one life you may be subject to cruelty in the next. An eye for an eye, a tooth for a tooth. I personally think that it is more of a superstition. It seems that most people that have good karma are happy but usually self-absorbed and egocentric. People with bad karma usually don't even realize it or wonder why life is always bringing them down. The people that can rationalize the good/bad karma and what it means are usually the people that deceive you. That's how karma works, I think....