Fix It in Post

"Post" naturally refers to "post-production", the part after principal photography where all the editing, sound-looping, Special Effects etc. happen.

"Fix it in Post" is said when you goof, but decide you don't want to re-shoot. "Forget it, we'll fix it in post" they say and move on with their lives. In post-production they will edit out the mistake, loop dialog to cover it or digitally re-master the image so the mistake never happened.

These are the four worst words to hear on any shoot—not only are the actors and crew tipped off that something bad is happening, but the editor knows that their job has just gotten 200% harder.

Examples of Fix It in Post include:

Spoofed in the extremely-fun "Wormhole X-Treme" episode of Stargate SG-1. A real alien spaceship comes down to pick up some stranded alien beings in the middle of a Show Within a Show written by another alien, based upon hazy memories of the SGC. While two of the production crew (who actually are real production crew on Stargate) are talking about it, they say that the special effects were a little weak, and that "We'll fix it in post." Then they go to play some golf.
An out-take from the fourth series of Red Dwarf: Cat (Danny John-Jules) and Lister (Craig Charles) are in a tight spot—when Lister pulls out his lighter, they find themselves in what appears to be a small cave. Craig Charles says "Stone," and taps the wall, which makes a very obviously hollow wooden sound. The audience immediately cracks up. Danny starts laughing as well, and Craig shouts at the audience: "They were gonna sort that out in the dub!"
In Home Movies, Jason once complains that Brendan is always saying this, even though Brendan never actually fixes anything in post. It's likely that Brendan doesn't actually know what this term means and that this is just one of the terms he throws around to sound like a real director (such as "print!" even though he's shooting on video).
Averted (sort of) in Manos: The Hands of Fate, almost every mistake was going to be Fixed In Post, but never was.
Seen in Dangeresque 3. The Cheat's special effects were going to be put in the post. It never happened.
In Disgaea 2, recurring foe and fallen TV star Axel once blows off the idea that he'll probably lose to the party again with this line.
In Planet Terror, a zombie ruins an otherwise perfect take by grabbing for Rose McGowan too soon, so Robert Rodriguez just fixed it by blowing his head off.
Linkara says this in one video review after he attempts to use one of his Running Gags, only to get an entirely different one.
A Running Gag in Total Drama Island Fanfic Total Drama Chris is Chris's failed attempts to invoke Manipulative Editing by claiming they'll cut out anything that's too revealing/implicating/unflattering in post. Obviously, this didn't happen.
Played straight near the beginning of Hannah Montana: The Movie, where the director shooting Hannah's music video invokes the trope word for word.
Seen often on game and panel shows filmed live, wherein, after a failed or very dirty joke, the teller says aloud that they'll take it out in post. Of course, they leave it in...
From the Riff Trax of Birdemic:

Mike: We're going to make this look good in post(-production) right?
Bill: The hell is post? Keep flailing!

A group of Drexel 3D animation students called their team We'll Fix It In Post productions, poking fun at the phrase. Their animation was featured on Drexel's site for some years, but has since been removed in favor of newer works.