http://www.freerepublic.com/focus/f-news/1689962/posts
yitbos - Mystery. Speculation includes something to do with frat boys, a Skull and Bones reference or even something Masonic, to a lame prank phrase used by posters to suggest they’re members of a special clique. A modern day version of Killroy Was Here, perhaps. (thanks, Tinian)
.. or may mean You’re In The Brotherhood Of Soldiers/Sailors
Ahhh Soooo… Very scruitable!!!