Paul Thoresen appears again to drop a 55-gallon water balloon on a '94 Chevy LeBaron convertible; Dave and Richard Simmons have another animated interview, in which the fitness guru stands and sings on the guest chair; Richard also appears on another tension-filled edition of "Alan Kalter's Celebrity Interview"; in her first Late Show appearance in 13 1/2 years, Mary-Louise Parker plugs "Weeds" while Dave