Elegant Forkbomb

You wouldn't think the following innocent looking 13 characters could cause so much chaos.

:(){ :|:& };:

They are often referred to as "Jaromil's Forkbomb". When typed into the command line of a Bourne-Shell compatible terminal (such as bash or zsh), they create a repeating fork task that will very quickly bring your Unix-like system screeching to a halt.