This may be Sally Quinn's vendetta with CBS for pitting her against Barbara Walters in the morning news slot when she just didn't have the stuff--or it may be her latest attempt to selffulfill the title of this apology for her big flop. Whichever, she's still got her foot in her mouth, just like that morning when she warned Middle America they might be eating horsemeat with their Bordelaise and Beaujolais. . . . It wasn't just the big money and clothes allowance, the celebrity status or the cachet of being the first news anchorwoman that lured her from the Washington Post society page to the Big Apple: ""While I was on television I could have given a big party for Henry Kissinger"" without a reporter's conflict of interests. But along came those ""snotty little reviews,"" an ulcer and even a flash that ""no matter how smart or talented or attractive I might think I was, there was absolutely nothing I could do."" Back at the Post, ""I've often asked myself how CBS could have made so many mistakes. . . . "" These are scattered shots in a densely fogged-in self-absorbed gossip-ridden complaint. It's embarrassing to read if you have any sympathy at all for children or fools, but there's a rule for Quinn's kind of stardom--say anything you like about her, just say something.