One time, I had a part on stage with the my family. I unfortunately tuned out during my dad's part of the script, and when it was my turn to reply to a question he asked me, I didn't know where we were in the script, and said my lines that were supposed to be at the end of the demo.
Another time, speaking of giggle fits, we had a small "drama" of Samuel hearing the call of Jehovah in the night when he was a child. So, for the voice of Jehovah, we had a bro. offstage booming into the microphone "DAVID!". Except, he blew his line, and shouted "JEHOVAH!". Huge gales of laughter.
Another time, a sister, explaining that God wants his worshipers to be actively working, said "To Jehovah, it doesn't matter what we don't do, but what we do do!" (doo-doo) Me and my brother could not quit giggling for some minutes afterwards. (And everytime I watch "Young Frankenstein", Madeleine Khan has a similar line that makes me think of that nite.)