I'm enjoying this thread, having been frustrated by 'Operational Reasons' in the past. In my previous life a more useful pa would help me replan my day as I usually had appointments after my short flights. Flybe were generally quite good, one of the better ones being the copilot called in sick, a standby is in his car driving up from Birmingham (to Doncaster). At least we had a rough timeline.
My longest delay was in Dublin following a storm. I knew it was going to be bad - BA had canceled a lot of their morning flight, whereas Aer Lingus had not, and then when planes were not getting into Dublin ended up with planes and crew well out of position. The flight was due to depart mid-afternoon, and changed gates 9 times. Eventually, there were only two flights left, Manchester and Gran Canaria. We got lucky - Gran Canaria got cancelled and I still wonder where they found hotel rooms.
They called boarding at 23:45, and took out applause in good grace, but did point out we were not the first of the day... We then had to wait a bit for pilots (who thought they were off to Gran Canaria), and even longer for baggage loaders. We arrived into Manchester at 1;30, a long time after my last train home. Manchester had suffered from the same storms and hotels were not available. I ended up in a £150 Uber to Doncaster, which Aer Lingus reimbursed.
Fun times, that I don't expect to experience again.