I had a few week old Specialized Supercross a few years back (the white one, before the Enduros came out). Laid it flat in the back of the car, with another bike on top. Had sheets/towels etc in between to protect the frames. Or so I thought.
The other bike had a rather natty set of DMR V12s on it, which proceed to eat their way through the layers of towels and sheets, and into my downtube. To make matters worse, we had to drive over a couple of cattlegrids on the way to the trails – as the car bounced over them, the cranks moved, causing the pedals to eat various parts of my shiny SX frame!
Words could not express how annoyed I was, but I had nobody to blame but myself for being too damn lazy to take the pedals off and pack the bikes better! D'oh!