There's a video from Battlefield Hardline's animation director Tony Gialdini at the bottom to explain more, but the short version is that the team snuck in a range of weird comedy animation Easter eggs. They also bet on whose would be found first, Tony's three-handed effort won that wager.
The team won't say how many there are (only that "there are still quite a few out there") or how you unlock them. The only clue given away by Tony is that his Easter egg requires an empty reload, and won't be triggered by a tactical one.
Here's what's been found so far:
RPG No Work Good
Use the Force
The Three-Hand Trick
And here's Battlefield Hardline's animation director Tony Gialdini to explain a little more about what's going on: