A recurring nightmare for any waiter or waitress: You're starting your shift in a strange restaurant and know nothing about the place or the menu, or even where the kitchen is located. That's roughly the conceit of the Living Room's new production, The Accidental Waiter (see review, page 16), presented as a brunch-theater production at 2:30 p.m. every Saturday and Sunday through June 12, in the upstairs loft at Lidia's Kansas City (101 West 22nd Street). The $50 price tag ($35 for children under 12) includes a three-course brunch (tax and gratuity included), which goes from 10:30 a.m. to 1:15 p.m., and the one-hour comedy. You'll need a reservation; call 816-221-3722. "I've seen the rehearsals, and the show is hilarious," says Lidia's manager Jason Connor. "There's improvisation, music and a little bit of Buster Keaton."