Nominations for Worst Platinum Happy Hour
While my experience is mostly limited to Asia, I have to give my vote to the Sheraton Hotel & Towers in Hong Kong. I am sitting here right now, it's 5:45pm (it starts at 5:30pm), there are dirty dishes everywhere, empty wine bottles, the two hot hors d'oeuvres are stone cold and greasy, the tables are dirty and and the staff is not what I would call 'proactive'. There's a guy in the corner in a semi-stupor who seems mind numbingly drunk and/or mentally unstable.
Close second: St. Regis Singapore.
IMHO, Le Meridien's seem to do it best.