AMARILLO: Oprah Winfrey ought to know that the state that used to hang rustlers and horse thieves is no place to to be reckless with insults. When she turned vegetarian on the air last year during a piece about mad cow disease, cattle prices plummeted. Along with 12 other ranchers, cattle feeder Paul Engler (who lost $6.7 million as a result) is now suing Winfrey under a 1995 Texas law that protects agricultural products from slander. Her fateful words? "It has just stopped me cold from eating another burger!" No point in horsing around. Winfrey may be able to settle the dust by promoting burger magnate Dave Thomas' opus "Well Done" on her next Book Club show.