When the person who lights the joint and takes the first puff also finishes it off, it is known as a "bookend". If another person finishes it off but they did not light the doobie, it is called a "bookmark".
A vapish dolt. An unruly sort whose behavior is often associated with staring off into space for no apparent reason, comfortable watching the grass grow, spending all day in bed looking at the ceiling.
man 1: Look at that dude over there, eatin' his fingernails and starin' at the floor.
man 2: Yea man, that dude is a bookend, ain't nothin' goin' on in his life.