Sometimes these requests ask that you copy the post and do something specific or unique to you, sometimes they ask you to post a coded message, like an inside joke, a dollar total derived from a list of illicit acts that are assigned specific values or a silly phrase that is made up from portions of text that are pieced together from a list using your date of birth or letters in your name.
The act of re-positng the request and/or complying with these given instruction or essentially, following the leader, is netsheeping or more formally, social netsheeping.
An example of a social netsheeping "game" or code would be a message sent instructing friends to post a phrase (without any explanation) in their facebook status, that is derived from a code:
In one example, a person wearing a black shirt, born on Jan 1, xxx0 would post, "I kicked a birdbath in your bathroom because that's how I roll!"
Search "current Facebook status game" or "I kicked a banana in your car because I'm cool like that" for more examples or actual codes used.