Comedian Brian Posehn, who describes himself as farts in man suit, has a comically menacing presence. With his six-foot-six frame, bald pate, black-rimmed glasses and wily beard, Posehn literally looks like the worlds scariest nerd. But hes one of the nicest guys in alternative comedy today. Since coming out of Sacramento, California, in 1992, Posehn has been an integral part of a variety of major comic enterprises. Hes appeared on Mr. Show, Reno: 911, Tom Goes to the Mayor and The Sarah Silverman Program. Posehn is also a member of The Comedians of Comedy, a tight-knit group featuring Patton Oswalt, Maria Bamford and Zach Galifianakis. During his live stand-up shows, he tends to focus on his life as a married, metal, straight-up nerd. 8 p.m. Thursday, 8 and 10:30 p.m. Friday and Saturday. The Improv, 7620 Katy Freeway. For information, call 713-333-8800 or visit www.improvhouston.com. $20.