Comedy Showcase T. Sean Shannon, a performer and writer with boisterous, even doofus, charm is back in town for one brief, shining week of sets on the Loony Toons stage. Shannon ran off to L.A. some years ago and has done quite well. He got his little comedy act on all the little comedy shows on cable and did writing gigs for In Living Color and Comic Strip Live. But, he says, "They're canceled, so I'm on the road again. Network television's loss is the Comedy Showcase's gain." He's glad to be back in good old Space City. "I love the Astros," he says, "but they'll probably be on strike." And then, with genuine sadness, "That's a bummer." Clearly, fame and fortune and La La land have not kept our boy from keeping up with the home team. Asked about his current act, Shannon says, "I don't want to give away any of the few bits I've got going for me," but does note that everyone loves his bit explaining that America is going downhill. "It's obvious," he says, "because the insane are now bland. We've got postmen snapping, chemistry teachers shooting people. The insane criminals are becoming dull." He longs for a finer time, an America with psychotics one could really be creeped out by. See Baby T, a nostalgic patriot. You can see him twice nightly Aug. 17-21. Tue.-Thu., 8 p.m.; Fri. & Sat., 8 & 10:30 p.m.; Sun., 8 p.m. Comedy Showcase, 12547 Gulf Fwy, 481-1188. $6.50-$8.50.