Two come to mind. Alitalia FCO-CDG... flight itself wasnt' bad at all. It was trying to get on it that sucked although in comparison to other nightmares it was minor. On honeymoon and taking the early flight out of Rome to Paris to have a full day. Had I known about morning fog in Rome I woulda gone to PAR the night before! The 6 morning flights, cancelled. After two hours of trying to get my luggage back (and finally succeeding) I managed to bludgeon groundstaff into endorsing my tix over to AF. Made zero difference... except now the groundstaff were contract and cared even less. In the end we got punted BACK to Alitalia and on the 1 PM flight when we shoulda been on the 6 AM.
It gets better. WE MISS THE FLIGHT. Being stupid Americans we trust the screens showing gate info and stay in the lounge. Only then do I find out that the posted gate was not only incorrect, it was 5 gate changes ago! We track down the right gate about 10 minutes after they close the door. Back to the lounge, lather, rinse, repeat. Rebooked on 3:20 flight. This time we learn and go to the gate an hour early. Same gate change gauntlet... except this time no one knows where they moved the flight. Finally wandering in desperation I see a line of people filing out a door down to a bus. Gate has ZERO info posted whatsoever. I go ask the GA if it's AZxxx and she nods. We kinda looked at each other and shrugged and figured if it wasn't we'd figure it out when we got wherever the hell the plane was going (it was the right flight). Only other issue would be that the MD-80 was almost as clean as the Flatbush Ave subway platform in New York and everyone stuffed everything they owned into the first four bins so we had no overhead space. The FA's just shrugged and strapped our hand-luggage to two empty seats. At least the beer was good.
Second was just flipping horrible. Flying AA from MIA to LHR. Despite knowing better I don't bother to check the seat out before we push. I'm so exhausted I crash out the moment I sit down and strap in. Wake up about 25 minutes after takeoff and go to swivel the seat so I can recline. No go. I call the FA, he can't get it working either. The manual controls don't work, so somehow the thing jammed. EVERY seat on the flight was full (overbooked) so they had no place to put me... so I spent what was supposed to be sleep-time sitting bolt upright for 8 hours. AA did make good on the flight though and gave me an MCO for the one-way cost of the ticket and the miles back from the upgrade. I'dve rather had the sleep though; I managed to reschedule meetings to the afternoon but was still a wreck.