One of the best was on the Wirral many moons ago. We had been clear with the church as to what we needed tech wise, back then it was as simple as an overhead projector, and the church had promised all would be fine. On the day there was no OHP so we had to pass our acetates around the congregation whilst we spoke. Priceless!
On another not so distant Roadshow, we were in a church where the vicar (an ardent Mac fan) decided to overrule the tech guy and interfere with the PC and our PowerPoint. Needless to say it didn't go well. 😂
I'll probably get told off for this but