Meaning
What does That’ll Do, Pig mean?
That’ll Do, Pig is a popular catchphrase, adopted from the legendary 1995 film, Babe, in which the protagonist is a pig, acting as a shepherd dog.
The phrase is utilized as a way of verbally patting someone’s head, but making sure, that they don’t fly far from the ground, rather stay modest about their success.
To my great disdain, there are no current applications of the phrase in image macros, related to policemen, which is a huge opportunity missed by the online meme community.
Origin
What's the origin of That’ll Do, Pig?
The sentence can be heard in the final scene of the movie, where the pig, acting as a shepherd dog wins the shepherding contest and sits humbly next to his owner, who then says the phrase with a smile.
Spread & Usage
How did That’ll Do, Pig spread?
The term got great recognition, mainly because of how casually and stoically Mr. Hoggett, the pig’s owner reacts to that extraordinary situation.
Stoics and hard to impress people had adopted the phrase into their dictionary since then, allowing them to themselves away from too big enthusiasm.
Urban Dictionary has one of their entries on the phrase since 2011, while the other definition was written in 2017.

External resources
- shmoop – That’ll do pig. That’ll do.