How do you convince someone that communism is bad?

There are several steps involved:

1) You have to narrow down what you are talking about. Are you discussing the theoretical utopia imagined by Marx where there is anarchy and people freely give each other all of the resources that they need? Are you talking about a specific country and its policies -- if so, is it a Traditional Communist State (like the Soviet Union), a Leninist-Communist State (like PR China), or a Dynastic Communist State (like North Korea)?

2) What are you comparing -- personal freedoms, employment, economic growth, etc.?

3) Compare such data with a Western country of your choosing. Try to use actual reports and data so it is more difficult to oppose your analysis with simple hand-waving.