Most annoying: Seventeen hour delay in Shanghai because the military was using the airspace, including embarking and disembarking the aircraft several times.
Most depressing: 23 hours in Bombay, as the TG aircraft went technical. Bombay wasn't the world's best airport in which to spend a lengthy delay.
Best ever: Five days in Jo'burg because of ATC strikes in Europe (I think maybe France, specifically). The airline knew it was coming, and they actually contacted me and let me choose an alternative route back to the states. The earliest was on KLM in five days, so I spent a lovely time in South Africa doing day safaris and basically being a tourist, which I never really got to do otherwise. The piper was paid on the flight back, however, as the South-Africa to Europe leg was in coach, seated between two enormously fat French guys who drank until they passed out and then snored and farted continuously until we touched down in Schipol. It was like being in a loud, rubbery chife closet.