Years ago, my highschool group was in the midst of a serious RP arguement, with one of the players shaking his finger in another's face. It was getting really intense, and then the second player calmly hung a pretzel from the first player's finger.
Needless to say, after 8 hours of gaming, a bunch of high-school boys found that to be the funniest thing they'd ever seen. We were laughing so hard none of us could breathe, and it completely broke the mood. We went from that to more sedate monster bashing.
Funny or stupid? I don't know, but the image has stayed with me for 25 years.