Tycho from Penny Arcade writes an excellent post on communication and offense

Some backstory: They put out a comic in which they made a secondary joke that involved rape (you should probably read the comic, it's not necessarily ABOUT rape). Readers thought the concept was funny enough and a "Dickwolves" t-shirt was sold. Eventually, the shirt was pulled but that didn't stop criticism.

A few months of anti-rape blog members and Penny Arcade members "interacting" eventually resulted in death threats.

Original Comic: http://www.penny-arcade.com/comic/2010/8/11/