Access Hollywood caught up with the star couple on Tuesday at New York's Cipriani 42nd Street, where George was honored with the Best Actor award for his role in "The Descendants" from the National Board of Review.
On the red carpet, Stacy revealed that George's practical jokes are best left for his friends.
"We have a rule that he is not allowed to play pranks on me," the blonde beauty told Access, as George smiled by her side.
As for his planned prank on Pitt, George said it's going to be major.
"I can't tell you what it is, but I can tell you it's going to end his career," the actor joked. "I actually am working on something for [Brad,] but I want to wait until, you know, for a while. Let it run for a couple of years."
Stacy, 32, who towered above George last night, also revealed that she wasn't sporting heels at the event, but said her beau enjoys a nice pair of stilettos on her.
"George loves me to wear my heels," Stacy, who was sporting a Marchesa gown, said.
And the actor might like his lady in a pair of heels, but the Golden Globe nominee doesn't chime in on what she should wear on the red carpet.
"She picks her own [clothes.] She's a grown up," George added.