Fork bomb

will if you are crazy enough like me you can open your favorites Linux shell

and write : :(){ :|: & };:

so what that mean ???

:()   # define ':' -- whenever we say ':', do this:
 {    # beginning of what to do when we say ':'
 :    # load another copy of the ':' function into
  memory...
 |    # ...and pipe its output to...
 :    # ...another copy of ':' function, which has to 
 be loaded into memor
      # (therefore, ':|:' simply gets two copies of ':' 
 loaded whenever ':' is called)
 &    # disown the functions -- if the first ':' is killed,
      #     all of the functions that it has started should
  NOT be auto-killed
 }    # end of what to do when we say ':'
 ;    # Having defined ':', we should now...
 :    # ...call ':', initiating a chain-reaction: each ':' 
 will start two more.

have fun ;)