"Just the sausage please" is a reference to the game Cook, Serve, Delicious. It can be seen as a double entendre.
While playing CSD, Northernlion noticed that customers asked for a breakfast sandwich with "just the sausage, please" and started making jokes about giving people sausage. It briefly became a thing.
In the January 8th, 2014 stream, they played CSD again and Nick repeatedly chose the breakfast sandwich, saying he wanted to hear people ask for "just the sausage please."