I worked on a short film from 5pm until 10 on Saturday night, and then from 7am until midnight on Sunday. We shot on the second and fourth floor of a building that's been abandoned for over 80 years. It was a long shoot complicated by cast rescheduling and an uncomfortable (and arguably somewhat unsafe) environment. But it was awesome.
At the end of the day we finished loading the U-Haul and started saying our goodbyes. The last person I got to was the DP, with whom I had worked most extensively. We shook hands and said "Good working with you" and then stopped and looked at each other for a moment. We were both moving our mouths as if we each wanted to have the next word, but were too tired think of it. After about three seconds, he blurted out, "It's like joining the circus!" It's a comparison that's been made before, but it seemed appropriate at the time anyway.
It wasn't necessarily a funny thing to say, but I laughed quite a bit anyway, possibly out of sheer fatigue.