This program takes over the screen, prints flickering random characters and slowly makes the piped content (or input file) visible. Effectively, it does what hackers on tv-shows have.
Do this for example on Linux:
tree ~/Downloads | ./decrypt.py
jp2a my_favourite_cat.jpg --term-width | ./decrypt.py
ls ~/Downloads -R | ./decrypt.py
Recover some friend's hard drive (i.e.: he destroyed his mbr). After the "hard" work has been done, act like you are having a hard time and run some of his personal files through this program and ask if he recognizes the content.
Warning: keeps the entire input in memory and uses an O(n^2) algorithm. It is not efficient cpu/ram wise. Easy rewrite is possible but this is just for fun.
YouTube action shots - Thanks, Alex Willmer