I was watching this Defcon video and around 4:30 he shows a custom pattern of drive wiping  the drive is filled with a constant text pattern.Whether he is joking or not, is this possible? How would it be done using Linux's dd command?
DD with a specific pattern
dd;block device
The drive shown is filled with a repeating text pattern. This is dead easy to do. Not with dd, because dd doesn't do repeated patterns. There's no magic in dd, it's just a tool to copy bytes in slightly weird ways, which is very occasionally useful. The magic is in the block device (e.g. /dev/sda for a disk or /dev/sda1 for a partition). To generate a constant pattern, use yes:yes 'Now wouldn'\'' you like to know what was there before?' >/dev/sda(Don't run this at home! This is a command to wipe your hard drive. Also, note that in order to wipe the whole drive, you'd probably have to do it from an independent live system: if you wipe the mounted disk you're running from, the system is likely to crash as it tries to load bits of files and fails.)