After a half-hour of Juno MacGuff’s improbably glib one-liners, you wonder when the teenager ever shut up long enough to become pregnant. She has comebacks and putdowns for all occasions, supremely overconfident with her life awareness yet masking the fact that she doesn’t have a clue what to do next.

The bun in Juno’s oven is an accidental gift from her best friend. The words in her mouth are courtesy of Diablo Cody, an astonishing new screenwriter who needs to learn when to rein her gift a bit. Juno is relentlessly clever, enough to be annoying for viewers preferring “reality” to wordplay.

But with so many quotable lines -- the juiciest delivered by rising star Ellen Page (Hard Candy) - Juno ranks with Lars and the Real Girl as 2007’s most original screenplays.

After the crudeness of Knocked Up and the fairy tale feel of Waitress, the pregnancy topic would seem to be played out. Teen sex comedies featuring unwanted insemination are certainly old hat. Juno uses a bit of each, adds the few-holds-barred approach of a new writer who doesn’t know what she can’t get away with, and becomes a special treat.

Juno is slated to open Dec. 25 in local theaters.