Some of the best comedy provocatively pushes the envelope, and when done well, it can allow us to not take life too seriously. But sometimes it can go really wrong, and feel less like a keen observation and more just mean-spirited. There is a thin line that certain comedic movies walk between hilarious and offensive. As Tropic Thunder, with all its controversies, hits the theaters, I was reminded of other comedies in recent years that were met with some protest. Controversy doesn't always affect ticket sales, though sometimes over-the-line comedy seems to influence the way a movie is received. To see some examples, just hit "Start."