At your next barbecue, throw this info around, courtesy of Cory Bricker:
If you thought the term pig arose in the 1960s, you’re in for a surprise. The OED cites an 1811 reference to a “pig” as a Bow Street Runner–the early police force, named after the location of their headquarters, before Sir Robert Peel and the Metropolitan Police Force … Before that, the term “pig” had been used as early as the mid-1500s to refer to a person who is heartily disliked.
The usage was probably confined to the criminal classes until the 1960s, when it was taken up by protestors. False explanations for the term involve the gas masks worn by the riot police in that era, or the pigs in charge of George Orwell’s Animal Farm.
Then there’s JVC’s explanation: “I think [calling cops "pigs"] started because of the extreme similarity of body type—thick necks, obese bodies, etc, and how they both scrum on their food/victims.”7:56 am on April 24, 2014 Email Becky Akers