I haven't had any horrible experiences stuck on an aircraft (worst was a couple hours waiting to deplane on arrival in KEF due to high winds), but I did have a dog of a time on recent trip due to cascading delays.

Original flight was supposed to be LAX-AMS-BLQ on KLM. LAX-AMS got cancelled T-24 due to mechanical on the incoming plane (not a huge deal) and I was rebooked to LAX-SLC-CDG-BLQ with an earlier LAX departure. Made it to SLC, boarded a 2-week old DL A330neo, pushed back, then immediately towed back in reporting engine issues. We sat on the plane for about 90 minutes until they finally decided to deplane, and then had a couple more hours of rolling delays at the gate until the flight was finally cancelled to the next day. One moment of comedy where one of the mechanics working on the engine visibly threw up his hands in frustration. They strung along the cancellation long enough that it was impossible to make any other TATL that day, even connecting via the east coast. A night in a SLC motel later, finally departed via a replacement A330ceo after another 75 minutes of tech delays. That delay caused me to miss my connecting flight in CDG, resulting in yet another rebooking CDG-FRA-BLQ with last leg on Lufthansa.

I finally arrived in Italy sans-luggage ~30 hours after I was scheduled to get there - bag of course got lost on the inter-alliance transfer in FRA and would take another 3 days to make it to my hotel. Total transit time was 48hrs across 5 different aircraft when it was supposed to be an easy 14hr 1-stop. In hindsight I absolutely should have fought to keep the transatlantic flight ex-LAX rather than accepting the original rerouting, or worst case pushed for a domestic connection via a bigger SkyTeam intl hub like JFK or ATL.