It's often said that we on the West Coast are more apt to do lunch than to do irony. Clearly, no one told the folks at the Onion. The free humor weekly, founded 17 years ago by Wisconsin college students and now a New York institution, is planning a San Francisco edition that will be available in trademark green sidewalk boxes here by May. With its famously wry headlines (recent gems include "Caged Saddam to Be Highlight of Inaugural Ball" and "Americans Feel Safer With Martha Stewart in Jail"), the paper has long had a huge cult following, with a disproportionate number of its 4 million website visitors from the Bay Area (particularly Cal students). The S.F. version will have the same content found in its seven other city editions but will also include local band and theater reviews. So read it and weep with laughter, but don't do what several reporters have: take one of its stories as fact.