My two nominations would be

(i) Roy's in Woodland Hills - had the most disgusting meal of my life there - no comparison with the Roy's restaurants in Hawai'i, Monterey and Chicago, which are great - with appalling lighting, food tasting like cardboard, badly-handled wine, rushed service, rude valet parking attendants..... And now, God help me, because I complained I can't get off their mailing list.

(ii) Valentino in the Venetian in Las Vegas. Overpriced, badly-cooked food, a sommelier who argues with you when the wine is corked.....