"Your bailey's in the hallway', originates at Hoffman Estates High School, from some weird ass theater people, and is another in a long line of euphemisms for saying "your fly's open", or more specifically, "your dick's showing"
(Though, I have never had the opportunity to use it that way)
Tom: Hey! Dude! Your Bailey's in the hallway!!
Zach: Oh, yeah. must hvae forgot to put it in after I went to the bathroom