In Starwars: Return of the Jedi, during the assault on the second Deathstar, the Evil Emperor lures the Rebel forces into a trap.
The Master of the Obvious, and Admiral of the Rebel Fleet, Admiral Ackbar exclaims "IT'S A TRAP!", after one of his subordinates says "Enemy Ships in Sector 47!"
This is fundamentally the greatest Star Wars line, and one liner ever.
Usage is widespread.
"Sir Enemy Ships in Sector 47!"
"IT'S A TRAP!"