I had a low speed off way back when with the girlfriend on the back. No big deal and it didn't put her off marrying me but...
My biggest fright was as a puny 18yrs apprentice shipwright, I was coming home from my birds house when I saw one of my workmates staggering home drunk. I stopped and asked if he wanted a lift (always seemed to carry a spare lid then). Big Stan gets on the back.
Now, I was 5'8 and about 11stone, Big Stan was about 6' 8 and around 20 stone, extremely drunk and wobbling all over the place.
Never came off, but the worst 5 mile pillion ride I've ever done.