Longest Delay
 

Currently sitting in YYT waiting for thick fog to finally lift. I'm now into my fourth rebooking as almost no flights have gone in or out since Friday. Assuming I get out tomorrow it will be about 98 hours later than originally scheduled.

Curious to know what is the longest delay that others have waited out?

2.5 Hours on a Chicago-London Flight due to snow at ORD.

Longest Delay
 

Longest I ever had was a 24hour delay on an Air France flight from YUL to CDG back in 2007, I was travelling with my brother, so the name of the game was cheap.

Never again did I cheat on Star Alliance

Longest Delay
 

12hrs at LHR due to fog. As a percentage of true flying time; GSO to EWR 5hrs for a 1hr 10 min flight.

8 hours in SFO due to typhoon in HKG. 7 hours in ORD on my way to NRT due to mechanical issues.

Wow, the OP's 4 day delay makes my longest look like nothing, but I was once delayed in ORD for 20 hours due to a mechanical on the UA ORD-HKG flight.

Fog had me sit for 17 hours at MFM (Macao), all post-security. What a sordid affair that was, in February 2005.

Oh, and then Air Asia continued to give me delays, but at least (back then), they offered a night at the Concorde Inn at KUL too. Good papaya it was.

98 hours though, that's, that's a tough one.

Ah the joys of YYT. That's my home town and I am always nervous going home for Christmas because you can easily get stuck there for days on end. A few years ago my family was supposed to meet me and got fogged in for about 72 hours. They were less than pleased....

48 hours after an FR crash/hard landing blocked the runway at CIA.

24 hours following freak winds then the EK aircraft going tech at GLA.

I imagine folks who have been through a major disaster due to weather, warfare, etc., can beat this easily... or should "delay" be defined more narrowly?
My longest delay was 3 days due to hurricane. Also had family members delayed over a week due to volcano.

5 hours sitting at Melbourne airport because Qantas A380 air conditioning needed servicing.

Not sure if it counts, but 11 days due to the volcano in 2010.

We did not spend it all sitting in the airport, mercifully.

6 hours for a 45 minutes long flight BHD-MAN.

delayed 13 hrs for a 45 minute flight. would have been faster to take a bus. the airline is no longer in existence

I was delayed by Hurricane/Superstorm Sandy for roughly 18 hours before I finally just gave up and drove 12 hours to my destination.