At 10000ft when I was flying at the regionals I used a few of these...

Let the beaver off the bench.

Let the crack in back do the snack attack.

With a wave of the hand I'd say, "She means nothing to me".
(Thx Brian)

Release the hounds.

Of course we've all used the "aisle donkey" reference.

When asking the FO to talk to the pax I'd ask him/her to "Stroke the Toads". This came from the fact that all the passengers faces were green and you could just see their heads above the seat and their hands holding the seat in front. A metro liner reference.

Now I'm much more mature and ... Wait, no I'm not.