to be put on notice; to be called out. to be served is an open invitation to serve back. unless you can serve back in equal or better fashion, then you got owned and have been bumped in ranking. to be served originates from being served with documents that you need to appear in court.
Me and my b-boy crew were pop-lockin and chillin, then this other crew came up and tried to serve us, but we had better moves, so those bitches got served back and owned.
A hyped word that has been used at an increasingly appalling rate ever since that stupid movie "You Got Served" came out (and South Park made fun of it), giving cultureless and frequently rejected Internet geeks a relatively attractive cliché to dwell on for the next few months or so.
People use the word "served" in a pointless attempt to convince others that they are capable of staying aware of and using current buzz words.