By picking the dungeon in the first place.
Our groups tended to keep things light and entertaining, so nothing we did was ever truely terrible, but this game rapidly devolved from exciting to humurously bad, to tedious and depressing.
Right around 4:00 a.m was the time when we where getting really tired and not having fun any more, but by that point we had all hit the stubborn-drunk phase and wheren't thinking clearly enough to quit. And the GM wasn't doing us any favors because they were also stubborn-drunk, and was getting frustrated by our continued incompetence.
It was meant to be a "rousing good time" and instead ended up as the revelation of "wow, we really REALLY suck at this".
Maybe I should append that line to my original post.