Karma is the poorest reason to explain why things happen to bad people or why good things happen to good people. Why do people ignore the fact that good things happen to bad people and bad things happen to good people just as much as vice versa? People notice this kind of thing because it fits their idea of justice, so they explain it by saying the word, "karma," and they think they have conveyed an intelligent idea. There are numerous examples of good people who just have a lot of horrible things happen to them, and bad people get away with stuff and have no problems. Karma is a stupid term to address life's complex or random happenstances.
The phrase, "what comes around goes around," is perhaps a little better, but it still doesn't tell the whole story. People seem to say these things like they are scientific laws. What may be more accurate would be the phrase, "There are consequences to people's actions." For example, if you are a jerk to people, and you get fired, it is not because of karma, rather because you are a jerk.
That's my rant on karma. Thanks for listening. Please feel free to tear my argument apart now.