Yeah, sure, Shel Silverstein's crowning accomplishment might be "A Boy Named Sue," the hilarious song popularized by Johnny Cash, but the famous humorist also wrote a bunch of killer short plays. They'll be staged starting this weekend at the Vortex Theatre. Yes, many of them step way over the line, so don't bring the kids. Adults, though, can expect to laugh their asses off. Fridays and Saturdays at 8 p.m. $10 general, $8 students/seniors. Sundays at 6 p.m. $8. Runs through Jan. 23. 247-8600.