Cliff's long-estranged father (Dick O'Neill) comes into Cheers with a vital message. Still seething over the fact that his dad abandoned him years earlier, Cliff (John Ratzenberger) refuses to identify himself. But the elder Clavin knows just the right buttons to push, and push them he does. Meanwhile, Sam (Ted Danson) tries to keep his new date from meeting Diane (Shelley Long). ~ Hal Erickson, Rovi