I do love dungeons. Even one you've been in dozens of times can be full of surprises depending on your group.
Tonight that most innocuous of dungeons Utgarde Keep had disaster after disaster. Loken? The annoying dragon rider kept re-setting and people died. Tsk. At least everyone took it well.
Here's a snippet from Hellfire Ramparts I think where things went bad (everyone died) but it was all mellow (click to enlarge):
More often it goes like this: