A code word for sex. To be used in situations in which another person should not know what you are talking about. Other phrases include; building a white bookshelf (oral sex), staining a bookshelf (sex while girl is on period), and building a brown bookshelf (anal sex)
guy 1: "hey bro you build that bookshelf yet?"
guy 2: "straight up man! it went together real nice!"
parents: "its nice to see our son getting interested in books and carpentry"

guy 1: "are you going to be building a bookshelf this afternoon?"
guy 2: "yea so stay outta my room!"
by dr. carpenter man March 27, 2010