While messing around with Raspberry Pis, Docker, bridged networks, wireless networks, etc. I managed to bork my Pis. If this happened at home, I could use a serial console cable, or plug the Pi into the spare HDMI port on my monitor and use a USB keyboard, or attach a USB SD card reader to another Pi. Unfortunately, this happened at work, where I have no Pi console cable, no HDMI monitor (one downside to the Apple Thunderbolt Display), no USB keyboard and no USB SD card reader (although since I borked both Pis, the SD card reader would have been useless).
I did have my Macbook Pro and its SD reader, and several Ubuntu Vagrant boxes (running on VirtualBox).