I was sitting in a lawn chair, and had the TX on my lap, but with my hands underneath it. I had it angled down so the antennae was pointing towards the floor. In that position, the IU switch rests gently on my leg.

One day, I was coming in for a landing, and just as the skids touched the floor, I must have moved just right, and my leg pushed the IU switch forward. My BCP did the funky chicken dance for several seconds until I turned the TX off. It was only after this that I realized what had happened

I no longer fly with the TX sitting on my lap... I was planning to mod the TX so I could arm and disarm the IU switch at will, but just haven't ever gotten around to it. Maybe I will do it one of these days...